United States Patent l 191
`
`
`Wegwerth et al.
`
`[11] 3,922,440
`[45J Nov. 25, 1975
`
`F. Lesmes
`(54] SAFETY GLASS LIGHT CONTROL
`Primary Examiner-George
`
`T. McDonald
`
`Assistant Examiner-Alan
`MEDIUM
`
`
`
`
`Sell, Steldt & Attorney, Agent, or Firm-Alexander,
`Maplewood;
`[75]Inventors:
`Arthur A. Wegwerth,
`DeLaHunt
`White Bear Lake,
`R.Dean Lowrey,
`both of Minn.
`
`[57]
`
`ABSTRACT
`
`[22]Filed:Aug. 16, 1974
`
`[21]Appl. No.: 497,930
`
`
`
`.....................
`
`(73] Assignee:
`
`Minnesota Mining and
`A humidity-resistant shatter-resistant light control me­
`
`
`
`St. Paul,
`Manufacturing Company,
`
`
`dium comprises a light collimating film with cellulose
`Minn.
`
`
`
`
`acetate or cellulose acetate-butyrate surfaces having
`
`
`
`bonded to those surfaces a polymeric adhesive ob­
`
`
`
`tained from the polymerization of monomers compris­
`ing
`I. 50-80% by weight total monomer alkyl acrylate
`
`[52]U.S. Cl. ................ 428/437;
`428/412; 428/515;
`having I to 8 carbon atoms in the alkyl
`
`
`428/481; 428/483; 428/50 l; 428/913
`
`
`substituent and/or tetrahydrofurfuryl acrylate;
`(51] Int. Cl.2
`B32B 17/10; B32B 27/42;
`.
`
`
`2.20-50% of monomers further comprising
`B32B 27/30
`a. 0 to 50% by total weight of monomer
`
`
`[58]Field of Search ....... 161/199, 6,257,248, 183,
`N-alkylacrylamide and/or
`161/231
`
`N-alkylmethacrylamide, wherein the alkyl
`
`groups thereof have I to 8 carbon atoms, and
`References Cited
`
`b.0 to 50% by total weight of monomers
`UNITED STATES PATENTS
`N-vinyl-2-pyrrolidone,
`Steel ............................... 161/199 X
`
`
`4/1961
`2,980,567
`
`
`the adhesive layer further bonded to a transparent,
`
`Brown et al. ...................... 260/80.5
`11/1966
`3,285,888
`
`
`protective covering material.
`8/1970
`
`Olsen ...................................... 161/6
`3,524,789
`
`
`Beckmann et al.................. 161 / I 99
`3,658,636
`4/1972
`
`3 Claims, No Drawings
`
`
`Blank .............................. 161/199 X
`10/1973
`3,762,981
`
`( 5 6]
`
`MASIMO 2009
`Apple v. Masimo
`IPR2020-01526
`
`

`

`3,922,440
`
`1
`
`SAFETY GLASS LIGHT CONTROL MEDIUM
`
`Film or sheet materials with parallel louver elements
`or ordered louver elements are known to be able to
`
`provide directional control over penetrating visible ra-
`diation. Light is allowed to pass through such films or
`sheets only within a controlled angle of incidence. Such
`films and methods of manufacturing them are shown in
`US. Pat. No. 3,524,789 and U.S. application Ser. No.
`284,403, filed Aug. 28, 1972, now abandoned. These
`light control films are generally comprised of a trans-
`parent synthetic resin binder and arranged louver-like
`elements which are distributed within the binder in an
`
`organized light screening'or light collimating fashion
`(parallel to each other and normal to the surface or
`parallel to each other and at a defined angle to the sur-
`face of the sheet).
`Two limitations exist in the use of the films, mainly
`because they are thin sheet materials: (1) they are by
`themselves not capable of structurally withstanding ex—
`treme stresses and surface abrasions, and (2) they are
`subject to distortion from physical stress and tempera-
`tures. As it would be very difficult and expensive to
`make a light control film of sufficient thickness to be
`structurally sound and because this would still not im-
`prove the tendency of the surface to abrade, it is neces-
`sary to reinforce the sheets in another manner.
`Reinforcement of light collimating film materials
`presents a number of problems peculiar to the product
`and to the materials used in the product. Whatever the
`means of reinforcement,
`the problems of structural
`weaknesses and surface abrasion must be overcome
`without adversely affecting the optical properties of the
`film. A structurally sound light control film serves no
`purpose if it is highly distorted, poorly light transmis-
`sive, and undergoes permanent color changes under
`the influence of light. It is also necessary that any struc—
`turally reinforced light control film be able to withstand
`tests established as industrial standards for particular
`types of uses of such light control film. For example,
`the automobile safety glass industry has developed
`standard tests which are described in Federal Motor
`Vehicle Safety Standard 205 of the National Motor Ve-
`hicle Safety Act of 1966. These tests include minimum
`requirements applicable to safety glass for withstanding
`humidity and temperature extremes.
`It is therefore one aspect of this invention to provide
`a structurally sound, undistorted light control panel. [t
`is another aspect of this invention to reinforce light
`control film by laminating such film between two other
`sheet materials by means of adhesive.
`Further aspects of the present invention will be un—
`derstood from the following discussion.
`Light control films can be made of many different
`synthetic resinuous materials. The most preferred ma-
`terials, and the only materials with which the present
`invention is concerned are cellulose acetate and cellu-
`lose acetate—butyrate (i.e., polymeric films the polymer
`of which is at least 80% by weight of these materials).
`These materials are preferred by the industry because
`of their utility in known processes of manufacturing
`light control film as well as their desirable optic proper-
`ties. The desirability of these two materials as light con-
`trol films adds but another problem to the reinforce-
`ment of the films in that such materials do not generally
`adhere well to materials useful as adhesives. Further—
`more, these films have a relatively low melting temper-
`
`2
`ature (~235°C) and will therefore also tend to distort
`more rapidly than other film materials under many pro-
`cessing conditions. This further restricts the materials
`which may be used as adhesives for securing the light
`control film to a structurally supporting surface.
`Only one particular class of adhesive has been found
`to provide all the necessary properties for bonding cel-
`lulose acetate and cellulose acetate—butyrate films to
`supporting surfaces such as butyral coated glass or
`resin surfaces. The broadest class of resins useful in the
`practice of this invention are thermoplastic polymers
`derived from monomers comprising 50—80% by weight:
`1. alkyl acrylate having 1
`to 8 carbon atoms in the
`alkyl substituent thereof; and/or
`2. tetrahydrofurfuryl acrylate.
`20 to 50 by weight monomers further comprising:
`l. O to 50% N—alkylacrylamide and/or N—alkylmetha—
`crylamide, wherein the alkyl groups thereof have 1
`to 8 carbon atoms, and
`2. 0 to 50% by weight N-vinyl-Z-pyrrolidone.
`Most of these resins are disclosed in U.S. Pat. No.
`3,285,888, issued Nov. 15, 1966 and are polymers of:
`a. 40—75 parts by weight of at least one member se-
`lected from (1) tetrahydrofurfuryl acrylate and (2)
`alkyl acrylates having 1—8 carbon atoms in the
`alkyl substituent;
`b. 15—45 parts by weight of at least one member se-
`lected from N-alkyl-acrylamide
`and N-alkyl—
`methacrylamide wherein the alkyl groups thereof
`have 1—8 carbon atoms; and
`10—30 parts by weight N-vinyl-2-pyrrolidone.
`Where the monomer (a) consists essentially of tet-
`rahydrofurfuryl acrylate, the proportion of N—vinyl-
`2-pyrrolidone may vary from O to 30 parts per
`weight.
`The addition of other copolymerizable monomers to
`the polymer system tends to detract from the perfor-
`mance of the resin, but about 10% by weight of copoly-
`merizable, optically clear materials (e.g., acrylic acid,
`styrene and other ethylenically unsaturated monomers)
`may be used without extreme deterioration in the prop-
`erties of the adhesive. Where the cellulose acetate or
`cellulose acetate butyrate light control films are to be
`bonded between transparent thermoplastic sheets (e.g.,
`polycarbonates, acrylic resins, methacrylic resins, poly-
`esters, etc. ), a single film of the above adhesive, applied
`with minimum solvent, as by the use of a preformed
`thermoplastic adhesive film, is completely satisfactory
`in bonding the light control film to the sheets.
`Where the cellulose acetate or cellulose acetate-
`
`c.
`
`butyrate film is sandwiched between glass sheets, it is
`necessary to use a polyvinyl butyral resin (comprising
`at least 80% of polyvinyl butyral by weight solids and at
`most 30% by weight plasticizer) between the adhesive
`on the light control film and the transparent glass sheet.
`U.S. Pat. No. 3,285,888 which discloses adhesive
`compositions useful in the practice of this invention
`teaches only the usefulness of those adhesives on sur—
`faces such as highly plasticized polyvinyl chloride, steel
`and canvas. It is surprising that these adhesives have
`been found to provide the strong adhesion and other
`critical parameters necessary for bonding cellulosic
`light control film to other transparent surfaces.
`Federal Motor Vehicle Safety Standard 205 of the
`National Motor Vehicle Safety Act provides a number
`of tests for tinted laminated safety glass. U.S.A. Stan-
`dard 226.1-1966 of this Act provides three tests which
`evaluate the most significant properties of safety glass,
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`3 ,922,440
`
`3
`shatter resistance and humidity resistance.
`Tests 3 and 4 of this U.S.A. Standard measure humid-
`ity resistance. In the former test, a standard specimen
`ofa 12 inch x 12 inch square (30.5 cm X 30.5 cm) are
`kept in a closed container over water for two weeks at
`120° to 130°F. Decomposition, formation of bubbles,
`discoloration and separation are then evaluated.
`Test 4 requires that a standard specimen be subjected
`to water at 150°F. for three minutes and then followed
`immediately by boiling water for two hours. The tested
`laminate is then inspected for any form of defect result-
`ing from the treatment.
`Test 12 of that standard provides a measurement of
`impact resistance and shatter resistance by dropping a
`1/6 pound (255 g.) smooth solid steel sphere from thirty
`feet onto a framed and secured laminate. Only mini-
`mum glass separation from the resin is allowed in the
`specifications of this test.
`In addition to the satisfaction of these functional test
`
`requirements, it is essential that the addition of the ad—
`hesive layers to the cover sheets and light control film
`not reduce the total visible light transmissivity by more
`than 20%. Such a reduction of light transmission would
`essentially render the composite undesirable as a win-
`dow.
`To examine a class of adhesive or specific adhesive,
`the tests were initially performed on an article compris-
`ing two sheets of cellulose acetate butyrate and the ad—
`hesive. If this article could undergo the test procedures
`with satisfactory results, an article comprising the glass
`sheets sandwiching the light control
`film was con-
`structed and examined. All adhesives were applied ac-
`cording to instructions provided for commercially
`available adhesives or generally recognized techniques
`for specially formulated compositions.
`The following adhesives failed to provide even initial
`securement between the films; that is, they provided
`almost no measurable bond (less than 1 lb/inch width)
`between the sheets:
`
`polyvinyl butyral resin
`ethylene-acrylic acid copolymers
`block copolymers of styrene and butadiene
`Other materials were used with unsatisfactory results.
`Rhoplex AC34 (a copolymer of polybutyl acrylate and
`methyl methacrylate) failed to provide a bond to the
`surface of the cellulose acetate—butyrate film after 7
`days at 70% relative humidity and 95°F.
`GT Butvar (a polyacrylate blended with polyvinyl bu-
`tyral) generated bubbles within the adhesive during the
`boiling water test. The bubbles diminished the optical
`properties of the film. When the adhesive was used to
`laminate the light control film to glass with polyvinyl
`butyral,
`the glass was found to separate too readily
`from the film when shattered, thus not providing im-
`portant safety glass characteristics.
`Poly(2-ethylhexyl acrylate) failed the humidity test
`after fourteen days, developed bubbles during testing
`and generally provided too weak a bond to the cellu-
`lose acetate butyrate surface.
`Commercially available polyethylene terephthalate
`adhesive separated cleanly from the film and failed to
`maintain any bond in boiling water.
`A copolymer of ethyl acrylate and acrylic acid did
`not provide sufficient initial bonding strength and also
`failed to provide any bond in boiling water.
`The general epoxy resin adhesives form good initial
`bonds but lose all bond strength at high humidity and in
`the boiling water test. Another class of adhesives, the
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`4
`cyanoacrylates, give strong initial bonds but fail in the .
`boiling water test. Polyurethane adhesives generally
`failed during humidity and boiling tests and/or devel-
`oped coloration which significantly reduced the trans-
`parency of the laminate (e.g., 30% reduction in trans—
`missiveness).
`invention can be con—
`Laminates of the present
`structed as follows: The adhesive is spread on a silicon
`treated release paper at 4 to 5 mils wet with a 20% by
`weight solids solution. The solvent is evaporated in a
`drying oven at 130°F. and then 250°F. A chipboard is
`placed in a metal platen and the adhesive is placed in a
`metal platen and the adhesive is placed thereon with
`the release paper next to the board. A cellulose acetate
`butyrate light control film is placed over the adhesive
`layer, and a second adhesive layer-release paper com-
`posite is placed over the film with the adhesive in
`contact with the light control film. A second chipboard
`and metal place sandwich in the unbonded structure
`which is then pressed at 100 psi and 280°F. for a few
`seconds, then cooled, and the release paper stripped
`from the laminate. The adhesive coated light control
`film is thus prepared for direct bonding to a clear resin
`surface.
`
`Bonding to a clear resin surfacing film can be accom-
`plished by placing the adhesive coated light control
`film between preformed thermoplastic sheets or par-
`tially curing therrnoset resin sheets and the unbonded
`sandwich of materials placed within a heated platen
`and pressed. With light control films having the louvers
`directed perpendicularly to the surface, temperatues of
`about 280°F may be used to bond the sandwich. With
`light control films having louvers not perpendicularly
`aligned with the surface, temperatures not exceeding
`240°F should be used to avoid random procession of
`the louvers towards the perpendicular.
`EXAMPLE I
`
`A safety glass-light control film laminate was made as
`follows.
`Two adhesive films of polymers prepared according
`to the method shown in Example 2 of US. Pat. No.
`3,285,888, having an original monomer
`ratio of
`(55/25/20) ethyl acrylate/t-butyl acrylamide/n-vinyl-Z-
`pyrrolidone, were formed by coating silicone release
`paper with a 5 mil wet coat of the resin solution and
`dried at about 250°F.
`A sandwich was then formed between these two ad-
`hesive sheets (with the release paper maintained on the
`outside surface of the sandwich) by placing cellulose
`acetate butyrate films against the interior surfaces of
`the adhesive films and a skived, louvered cellulose ace-
`tate butyrate light control element having 0° (perpen-
`dicular) louveres, made according to US. patent appli-
`cation Ser. No. 284,403, filed Aug. 28, 1972, between
`the two cellulose acetate butyrate layers. This five part
`sandwich (adhesive, cellulose acetate butyrate,
`lou-
`vered element, cellulose acetate butyrate, adhesive)
`was placed between metal plates with chipboard covers
`at 100 lbs/in2 at 275°F. for a few minutes and removed.
`Two glass sheets having one surface of each coated
`with polyvinyl butyral resin were placed in a platen
`with the uncoated surfaces against the plate surfaces
`with the five layer sandwich between the glass sheets.
`The unbonded composite was heated at l90°—200°F. at
`10—15 lbs/in2 for only sufficient time as was necessary
`to secure the layers; then the composite is cooled to
`room temperature. The final bond was secured in an
`
`

`

`5
`autoclave with 125 lbs/in2 pressure at 275°—280°F. for
`1% hours and then cooled in the pressurized autoclave.
`The product was subjected to the humidity and boil-
`ing water tests with no adverse results. The laminate
`also performed according to required standards in the
`shatter test. There was sufficient transmission through
`the safety-glass laminate product to enable its use as a
`window material.
`
`EXAMPLES II — V
`
`According to the above method of laminating safety
`glass products, four different adhesives within the de-
`fined adhesive class of this invention were used. The
`adhesives used were:
`.
`
`1. Ethyl acrylate/t-butyl acrylamide/n-vinyl-Z-pyr-
`rolidone (55/25/20) terpolymer.
`'
`2. The above terpolymer modified with the addition
`of less than 10% by weight total of a butadiene-
`acrylonitrile copolymer, malic acid, and natural es-
`ters of abietic acid.
`
`3. A copolymer of ethyl acrylate/t—butyl acrylamide
`(65/35).
`
`3,922,440
`
`6
`surfaces a transparent adhesive derived from the poly-
`merization of
`
`to 8
`1. 50—80% by weight alkyl acrylates having 1
`carbon atoms in the alkyl substituent and/or tetra-
`hydrofurfuryl acrylate,
`2. 20 to 50% by weight of monomers further compris-
`ing 0 to 50% N—alkylacrylamide and/or N-alkylme-
`thacrylamide with the alkyl groups thereof having 1
`to 8 carbon atoms, and O to 50% by weight N-vinyl-
`2-pyrrolidone,
`and secured to the adhesive a transparent synthetic
`resin or the butyral surface of glass bonded to an at
`least 70% by weight polyvinyl butyral resin coating.
`What we claim is:
`
`1. A humidity-resistant shatter-resistant light control
`medium comprising a light collimating film with cellu-
`lose acetate or cellulose acetate-butyrate surfaces hav—
`ing bonded to those surfaces a polymeric adhesive ob-
`tained from the polymerization of monomers compris—
`mg
`
`10
`
`15
`
`20
`
`1. 50—80% by weight total monomer alkyl acrylate
`having 1 to 8- carbon atoms in the alkyl substituent
`and/or tetrahydrofurfuryl acrylate;
`2. 20—50% of monomers further comprising
`a. 0 to 50% by total weight of monomer N-alkyla-
`crylamide and/or N-alkylmethacrylamide, wherein
`the alkyl groups thereof have 1 to 8 carbon atoms,
`and
`
`b. 0 to 50% by total weight of monomers N-vinyl-Z-
`pyrrolidone,
`the adhesive layer further bonded to a transparent, pro—
`tective covering material.
`2. The light control medium of claim 1 wherein the
`protective covering material
`is glass having an im-
`proved bonding surface of butyral resin against the said
`polymeric adhesive layer.
`3. The light control medium of claim 1 wherein the
`protective covering material is a transparent polymeric
`layer.
`*
`*
`*
`*
`*
`
`4. A copolymer of ethyl acrylate/n-vinyl-2-pyrroli-
`done (65/35).
`
`25
`
`All four composites were subjected to the humidity,
`boiling water and shatter tests, and all four composites
`passed. The adhesives were also colorless and reduced
`transmissiveness by less than 10%. All exhibited ac-
`ceptable peel strength (i.e., greater than 8 lbs. per inch
`width) and the first three adhesives exhibited peel
`strengths exceeding 15 lbs./in. width.
`The above examples show that only the presently
`cited class of adhesives have been able to perform satis-
`factorily in the light control safety glass structures pres‘
`ently described.
`A light collimating laminate comprising a light colli-
`mating, transparent, cellulose acetate or cellulose ace—
`' tate butyrate film having bonded on the opposed major
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