CA1258941A - Plasticized polyvinyl butyral interlayers process for forming same and plasticizer blend therefor - Google Patents

Abstract

PLASTICIZED POLYVINYL BUTYRAL INTERLAYERS
PROCESS FOR FORMING SAME AND PLASTICIZER
BLEND THEREFOR
ABSTRACT
In a polyvinyl butyral (PVB) sheet plasti-cized with a multiester of an alcohol having 2 to 4 hydroxyl groups and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule, which sheet does not craze polycarbonate or polyacrylate when in contact therewith, the addition of a synergistically effective amount of a monoester of a glycol and such C16 to C20 acid improves the low temperature penetration resistance and adhesion properties of such sheet without significant loss in its resistance to stress cracking polycarbonate or polyacrylate in a laminated glass assembly.

Description

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PLASTICIZ~D PULYVINYL BUTYRAL INl'ERLAYERS
-PROCESS FOR FORMING SAME AND PLASTICIZER
BLEND THEREFOR
BACKGROUND OF INVENTION
This invention relates to polyvinyl butyral (PVB) sheet plasticized with fatty acid esters and more paxticularly with a fatty acid ester blend which provides the sheet with improved penetration resist-ance without significant loss in its resistance to stress cracking polycarbonate or polyacrylate when in contact therewith as an interlayer in a laminated glass assembly.
In recent years sociologists and psycholo-gists have started a movement toward prisons without bars. Thick layers of impact resistant polycarbonate initially used in such applications were quite early determined to be inadequate since the polycarbonate could be burned or scratched or dissolved or fractured when heated or abused. Moreover, when exposed to the elements the polycarbonate turned yellow, lost its strength and was susceptable to crazing. Based on this early work a need was defined for a material for security applications which was strong, chemically impervious, and scratch and fracture resistant over a wide range of ambient conditions.
Thereafter laminates of one or more layers of glass with one or more layers of polycarbonate were proposed which in use were mounted with the glass layer on the outside exposed to the elements and the polycarbonate either forming the innermost surface or positioned inboard of a glass layer forming such innermost surface. ~owever, with these laminates an interlayer between the glass and polycarbonate is necessary since polycarbonate will not adequately adhere to glass.
Thermoplastic polyurethane layers have been used to laminate polycarbonate to glass but polyure-thanes are costly and usually require treatment of

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the glass with a primer coating before lamination.
Moreover, such polyurethanes are difficult to process into laminates because their low melting temperatures dictate the need for a batch type deairing operation with long exposure to vacuum for complete air removal.
Commercially available grades of PVB sheet are not acceptable as an interlayer to adhere polycarbonate to glass because the plasticizer in the PVB crazes the polycarbonate. To solve this a special barrier coating, as disclosed in U. S. 4,243,719, was proposed between the polycarbonate and PVB to keep the plasti-cizer in the PVB away from the polycarbonate. The PVB
is still necessary since the coating will not adhere to the glass and the PVB assists in absorbing energy on impacting. Such a coating must be pinhole-free for obvious reasons and moreover is costly in that it represents an additional layer in an already multi layered laminate which could be avoided if a plasti-cizer for PVB were available which did not craze the polycarbonate.
Sulfonamide and phosphate plasticizers for PVB which do not attack polycarbonate are disclosed in U. S. 3,539,442 and 3,406,086 respectively but PV~
containing such plasticizers can only be difficultly extruded in forming sheet since they tend to decompose at extrusion conditions and degrade the PVB.
: Certain esters which in natural form can be the major c~nstituents of castor oil are proposed in U. S. 4,128,694 as plasticizers for P~B which neither craze polycarbonate or polyacrylate nor deteriorate during extrusion of plasticized PVB.
However, such interlayers exhibit relatively high glass transition temperatures (Tg~ at the usual plasticizer loadings and marginal peel adhesion to polycarbonate which means the impact properties at low performance temperatures are also marginal. This has 0~ .

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precluded the use of such interlayers in security glass applications exposed to cold climates.
A need, therefore, exists in the art for a plasticized PVB sheet having the properties of those disclosed in U. S. 4,128,694, but which has a lo~ Tg and higher peel adhesion and therefore improved low temperature performance properties when present as a functional PVB interlayer in a security glass laminate.
Eligher peel adhesion (i.e. equal to or greater than 10 newtons per cm) is needed to maintain laminate integrity during and after laminate impacting. However, very high peel adhesion (i.e~ equal to or greater than 30 newtons per cm) can produce laminate failure due to breakthrough when the laminate is impacted. On the other hand, very low peel adhesion (i.e. less than 10 newtons per cm) can produce delamination on impacting, e.g. along the laminate edges.
SUMMARY OF THE INVENTION
In accordance with one particular aspect of the present invention, there is provided, in a PVB sheet plasticized with a multiester of an alcohol having 2 to 4 hydroxyl groups and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule, the improvement which comprises, in combination with such multiester, a monoester of a glycol and such C16 to C20 unsaturated fatty acid, the amount of the combination of multiester and monoester being from about 10 to about 55 parts per hundred parts of the PVB resin, and wherein the ratio of monoester to multiester is between about 1:1 to about 5:1.
In accordance with another particular aspect of the present invention, there is provided, in a process for the preparation of PVB sheet by blending polyvinylbutyral with a plasticizer which is a multiester of an alcohol having 2 to 4 hydroxyl groups and a C16 to C20 unsaturated fatty acid having a ~? ~?

hydroxyl group attached to the acid molecule and extruding the blend to form a sheet, the improvement which comprises adding to the blend a monoester of a glycol and the C16 to C20 unsaturated fatty acid, the amount of the combination of multiester and monoester being from about 10 to about 55 parts per hundred parts of the PVB resin, and wherein the ratio of monoester to multiester is between about 1:1 to about 5:1.
In accordance with a still further aspect of the present invention, there is provided a plasticizer blend for polyvinyl butyral comprising a monoester of a glycol and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule and a multiester of an alcohol having 2 to ~ hydroxyl groups and the unsaturated fatty acid, the amount of the combination of multiester and monoester being from about 10 to about 55 parts per hundred parts of the PVs resin, and wherein the ratio of monoester to multiester is between about 1:1 to about 5:1.
The monoester is preferably propylene 1,2 glycol partially esterified with ricinoleic acid.
DESCRIPTION OF PREFERRED EMBODIMENTS
U. S. No. 4,128,69~ discloses a plasticizer for PVB resin in the form of a specific fatty acid multiester of an alcohol having 2 to 4 hydroxyl groups and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule. The term "multiester" as used herein means an ester formed by esterifying more than one hydroxyl group o such an alcohol with such an acid~ Such plastici~er in a PVB
interlayer does not attack polycarbonate or polyacrylate when present in a multiple panel safety or security glass laminate assembly. In the present invention, a monoester species of such specific fatty acid multiester is combined with ~he latter to form a plasticizer blend for PVB which unexpectedly lowers L~ ~, -5- 06-12-(1089)~

the Tg of PVB plasticized therewith and incrementally improves the PVs interlayer penetration resistance and peel adhesion to polycarbonate ovex that obtained using the fatty acid multiester alone. Performance with polyacrylate is predicted to be similar. The plasticizer blend of the present invention, therefore, comprises a multiester component te.g. a triester~
combined with a monoester glycol component, each component being derivable from the same class of unsaturated fatty acidsO
The preferred multiester component of the plasticizer blend of the present invention is con-tained in castor oil which is a triglyceride ester of fatty acids. It comprlses a mi~ture of esters of glycerol with the following acids, (the figure in parentheses being the approximate weight percent of esters formed from that acid): ricinoleic acid (89.5%), oleic acid (3~0%), linoleic acid (4.2~), stearic acid 1% and dihydroxy-stearic acid. Approxi-mately 63.6% of the ricinoleate is triester, (glyceroltriricinoleate) 31.1~ diester and 5.1% the monoester.
The latter level of monoester in castor oil is insuf-ficient in itself to provide the improvement of the present invention. Other multiesters found useful wherein one molecule of the esterifying acid has reacted with each available hydroxyl of the alcohol are those based on triethylene glycol, trimethylol propane and pentaerythritol.
The unsaturated fatty acid monoester found synergistically effective as an additional plasticizer in combination with the preferred castor oil in PVB
sheet in property improving combination in a blend with the multiester referred to above is a monoester of a glycol and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule.
The preferred monoester is propylene glycol 1,~

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monoricinoleate. Though not certain of the reason, it appears that the unreacted hydroxyl group immediately ad~acent the acid linkage in the monoester plays an important function in the plasticizer blend insofar as 5 improving the peel adhesion to polycarbonate or polyacrylate of PVB interlayer plasticized there-with, as well as the penetration resistance of glass laminates made up of layers of these materials.
The acids that may be used to form the 10 multiester and monoester plasticizer components of the blend of the present invention have from 16 to 20 car-bon atoms and include in addition to ricinoleic acid, (12-hyroxyoleic acid) other hydroxy-oleic acids with the hydroxyl group located other than on the "12" car-bon atom such as 6~, 8-, 14-, or 16-hydroxy-oleic acid, 12-hydroxyelaidic acid and acids with the same em-pirical formula with the hydroxyl located on other than the "12" atom. Also included are the corres-ponding variations of 12-hydroxy-hexodec-9-enoic acid and 12-hydroxy-eicos-9-enoic acid.
A single acid may provide all the esterify-ing acid groups but usually a mixture of unsaturated esterifying acids, are used, provided that the ester-ifying acids together provide at least one unsatura-tion and one hydroxyl group per molecule of plasti-cizer.
The amount of plasticizer blend to be used in the laminate interlayer of the invention should be from 10 to 55 parts per hundred parts of P~TB resin (phr). The preferred amount is 20 to 50 phr and particularly preferred is 30 to 40 phr.
The weight proportion of monoester to multiester in the plasticizex blend should be between about 1:1 to about 5:1. When castor oil is used as the multiester, allowance may optionally be made for the minor level of monoester therein in determining :, ~5~3g~1 -7- 06-12-~1089)A

the total amount of monoester to be used in the blend.
It is preferred that the monoester be present as the major constituent of the plasticizer blend, i.e.
present in amount greater than the multiester. The most preferred proportion of monoester to multiester is 2:1.
The monoesters of the present invention are commercially available from CasChem Inc., Bayonne, New Jersey, 07002 under the registered trademark Flexricin.
The various grades of each used in the Examples following are identified in the footnotes to Table 1.
In general, the polyvinyl acetal resins employed may be considered to be made up, on a weight basis, of from 5 to 25 percent hydroxyl groups, cal-culated as polyvinyl alcohol, O to 4 percent acetategroups, calculated as polyvinyl acetate, and the bal-ance substantially acetal. When the acetal is buty-raldehyde acetal, the polyvinyl acetal resin will preferably contain, on a weight hasis, ~rom 10 to 25 percent hydroxyl groups, calculated as polyvinyl alcohol and from 0 to lO percent acetate groups, calculated as polyvinyl acetate, the balance being substantially butyraldehyde acetal.
The polycarbonate component may be any suitable sheet of polycarbonate such as disclosed in U. S. Patent Nos. 3,028,365 and 3,117,Ql9 and is preferably prepared by reacting di(monohydroxyaryl)-alkanes with derivati~es of carbonic acid such as phosgene and bischloro-carbonic acid esters of di-(monohydroxy-aryl)-alkanes. Commercial polycarbonate sheeting is available from General Electric Company under the trademark Lexan.
Where the resin sheet is a polyacrylate this may be as an ester of a lower aliphatic alcohol, such as butyl-, propyl-, ethyl-, or methyl alcohol and acrylic-, methacrylic-, ethacrylic, propacrylic-5~39~
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or butacrylic- acid. By far the most convenient is polymethyl methacrylate.
The plasticized interlayer of the invention can be used to make a simple laminate with the inter-layer in contact on at least one surface with apolycarbonate or a polyacrylate sheet. Vsually one of the surfaces of the interlayer will be in contact~
with a different material such as glass.
For security glass it is usual to provide multiple layers, such as four or more, comprising plasticized interlayers and polycarbonate or poly-acrylate layers and glass layers laminated together to form laminates of from 1/2 inch up to several inches in thickness. For such purposes the construction usually comprises glass/interlayer/polycarbonate or polyacrylate/interlayer/glass units multiplied as appropriate.
The laminates produced using the plasticized interlayer of the invention may be treated to reduce light transmission by tinting one or more of the com-ponent layers or by supplying a metallized surface to one or more of the layers. The treatment can be such as to produce a uniform reduction in light transmission over the whole sheet or perhaps in the form of a band or other form of localized effect.
Laminates formed according to the present invention are broadly useful in any application re-quiring a safety glass assembly such as in vehicular windshields, but are especially useful in security ap-plications such as prisons without bars and installa-tions requiring a somewhat lesser degree of security such as bank windows, cashier booths, jewelry counters and the like. Applications in which the laminates of the inventisn can be used are disclosed in U. S.
~5 4,243,719, col. 10, line 3 through col. 12, line 36.

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In addition to the plasticizers, the inter-layers of the present invention may contain other additives such as dyes, ultraviolet light stabiliz-ers, salts to control adhesion and antioxidants ~nd may, if desired, be treated with additives to improve laminating efficiency.
The invention is further described with reference to the following examples which are for illustration only and are not intended to imply any limitation or restriction on the invention.

Laminates of uncoated, general purpose high impact, glazing grade, polycarbonate (Lexan~ 9030) and PVB sheet were made using various plasticizers accord-ing to the following procedure.
The PVB used contained 18 weight percent hydroxyl groups (measured as polyvinyl alcohol) and had a solution viscosity o~ .23-.~5 ~a.s as determined by Kinemetic Viscometer, Cannon Fenske type (ASTM
D-4445). The plasticizer(s) was added to the PVB
resin and mixed either manually or with a low inten-sity laboratory mixer and allowed to sit overnight to promote absorption of the plasticizer by the resin. A
sigma blade mixer with steam for heating passing through the mixer jacket was then used for about ten minutes to melt and mix the resin and plasticizer and form molten crumbs of plasticized PVB.
The crumbs o~ plasticized PVB were deposited in a ~rame and pressed into blocks 35.5 cm by 40.6 cm of about 5 cm thickness. Slices of plasticized interlayer of about O.75 mm thickness were cut from these blocks and separated from each other via inter-posed plastic fllm, conditioned for about one hour at 20 to 35% relative humidity to control moisture level therein at 0.4 to 0.5 weight %.

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Initially washed polycarbonate (0.32 cm to 0.62 cm thickness) sheets and layers of commercially available float glass were u-sed in assembling each laminate as follows: a slice of plasticized inter-layer was placed on either side of the polycarbonate layer and then a layer of glass placed against each layer of interlayer. The loosely assembled laminRte was pre-compressed at about 4.576 MPa (45.7 kg/cm2) at temperatures of 100C.-215C. in conventional 10 manner usin~ a heated press, then air-autoclaved at 93~., .343 MPa (3.5 kg/cm2) for one hour, 10 min., followed hy 135C. and 1.274 MPa (13 kg/cm2) for one hour after which the temperature was reduced to 38C. for 20 min. whereupon the pressure was reduced 15 to end the cycle.
Other laminates for peel adhesion testing were prepared using standard laminating techniques familiar to those in the art except that an adhesive coated aluminum foil was substituted for one of the 20 glass layers and the glass and interlayer on the other side of the polycarbonate was eliminated.
Values for the various properties presented in Table 1 following were determined according to the following procedures.
The glass transition temperature (Tg) of plasticized PVB was measured using a Rheometric Mechanical Spectrometer which is a rectangular torsion test conducted in a nitrogen atmosphere at a constant frequency ~l-hertz) and temperature.
Compatability of plasticizer and PVB resin as determined by the extent of exudation of the plasticizer from the resin after melt mixing was visually noted by the absence or presence and level of free plasticizer either on the surface of the 35 plasticized resin or in the bowl of the sigma mixer.
Penetra~ion resistance of the glass-poly-carbonate-plasticized interlayer laminates was ~58~

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measured by dropping a 2270 gm steel ball five times from 2.4m onto the laminate which had been pre-con-ditioned for two hours at the temperature at which the test was run. The lntegrity of the sample inso-far as the extent, i~ any, of delamination along theglass cracks between the polycarbonate and interlayer was visually noted after five drops. The term "good integrity" as used in ~able l following means that some portion of the laminate, such as the edge area, had all components adhered together after testing.
Clarity of the autoclaved laminate as de-termined by haze level was visually noted~
Stress cracking of the polycarbonate by the plasticizer(s~ used in the interlayer was determined at 23C. and 70C. In this test the stress applied to polycarbonate specimens was increment-ally increased to 13.8 MPa while a patch saturated with the plasticizer fluid was applied at the point of maximum stress and the stress noted at which cracking occurred. More specifically, injection molded polycarbonate coupons in the form of beams about 2.5~ cm wide were loaded for a specified time, e.g. lO minutes, and then the patch saturated with the test plasticizer was applied to the point of maximum stress for an additional time depending on the temperature-i.e. 72 hours at 23C and 8 hours at 70C.
Peel adhes~on-two parallel grooves 4 cm apart were formed leng-thwise through the aluminum foil and interlayer. The polycar~onate at one end of the laminate a few cms in from the end was scored and broken perpendicular to the grooves. The outside edge of the aluminum foil and interlayer on each side of the 4 cm strip was cut at the polycarbonate break.
The foil, interlayer and cut polycarbonate were then clamped in the test grips of an Instron tensile tester ~ , ,..

, -12- 06-12-(1089~A
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and the force required to separate the foil and interlayer from the polycarbonate along the grooves measured at room temperature. A range of 10 to 30 newtons/cm is desired to provide the optimum balance of impact and delamination resistance in the laminate.
The results obtained are set forth in the following Table 1.

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Stress crack performance of the glycerol triricinoleate/ethylene glycol monoricinoleate blend of Example 7 is predicted to be equivalent to that obtained with the blend of Example 2 containing propylene glycol monoricinoleate.
The foregoing data indicates that when the multiester i5 the sole or principal plasticizer in the plasticized interlayer (Example 1) in accordance with U. S. 4,128,694, though stress crack resistance of the polycarbonate i5 good, the tendency to delaminate is high and therefore the penetration resistance is poor because of the relatively high value of Tg and low peel adhe~ion. When the lower molecular weight glycol monoester (Examples 3 and 6) was used alone, Tg was reduced and pentration r~sistance was improved, but at the expense of stress crack resistance of the polycarbonate at high temperature. However, when only a relatively minor amount (12.5-15 parts) of the multiester was added to the monoester, (Examples 2, and 7) acceptable stress crack resistance was obtained ~nd peel adhesion was significantly increased with respect to the propylene glycol monoricinoleate species of Example 2 without a reduction in Tg and in penetration resistance. This significant increase in peel adhesion and failure of Tg to increase with the addition of the multiester constituent to the mono-ester constituent was unexpected. The blend contain-ing a monoester of an alcohol having more than two hydroxyl groups, i.e. the pentaerythritol monoricin-oleate species of Example 5 and the glycerol monori-cinoleate species of Example 9, which are outside the scope of this invention, were deficient in color (Ex-ample 5) and compatibility (Example 9).
Though the plasticized PVB sheet of the invention can be formed by slicing from blocks as disclosed in the foregoing Examples, it is preferably ~ . , ~5~39~

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formed by extrusion mixing and sheet formation of the interlayer in a slot die.
The monoester glycol component of the plasticizer blend of the invention may comprise blends of monoesters, such as a blend of individual ethylene and propylene glycol monoester constituents.
While certain specific embodiments of the invention have been described with particularity herein, it will be recognized -that various modifica-tions thereof will occur to those skilled in theart~ The scope of the invention, therefore, is to be limited solely by the scope of the following claims.

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Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED
AS FOLLOWS:

1. In a PVB sheet plasticized with a multiester of an alcohol having 2 to 4 hydroxyl groups and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule, the improvement which comprises, in combination with such multiester, a monoester of a glycol and such C16 to C20 unsaturated fatty acid, the amount of said combination of multiester and monoester being from about 10 to about 55 parts per hundred parts of the PVB resin, and wherein the ratio of monoester to multiester is between about 1:1 to about 5:1.

2. The plasticized sheet of claim 1 wherein the monoester is propylene glycol-1,2 monoricinoleate.

3. The plasticized sheet of claim 1 wherein the monoester is ethylene glycol monoricinoleate.

4. The plasticized sheet of claim 1, 2 or 3 wherein the ratio of monoester to multiester is about 2:1.

5. The plasticized sheet of claim 1, 2 or 3 wherein the multiester is present as a castor oil component.

6. In a process for the preparation of PVB sheet by blending polyvinylbutyral with a plasticizer which is a multiester of an alcohol having 2 to 4 hydroxyl groups and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule and extruding the blend to form a sheet, the improvement which comprises adding to the blend a monoester of a glycol and said C16 to C20 unsaturated fatty acid, the amount of said combination of multiester and monoester being from about 10 to about 55 parts per hundred parts of the PVB resin, and wherein the ratio of monoester to multiester is between about 1:1 to about 5:1.

7. The process of claim 6 wherein the monoester is propylene glycol monoricinoleate.

8. The process of claim 6 wherein the monoester is ethylene glycol monoricinoleate.

9. The process of claim 6, 7 or 8 wherein the ratio of monoester to multiester in the blend is about 2:1.

10. The process of claim 6, 7 or 8 wherein the ratio of monoester to multiester in the blend is about 2:1 and wherein the multiester is present as a castor oil component.

11. A plasticizer blend for polyvinyl butyral comprising a monoester of a glycol and a C16 to C20 unsaturated fatty acid having a hydroxyl group attached to the acid molecule and a multiester of an alcohol having 2 to 4 hydroxyl groups and said unsaturated fatty acid, the amount of said combination of multiester and monoester being from about 10 to about 55 parts per hundred parts of the PVB resin, and wherein the ratio of monoester to multiester is between about 1:1 to about 5:1.

12. The blend of claim 11 wherein the monoester is formed from at least one member of the group consisting of ethylene glycol, propylene glycol-1,2 and mixtures thereof.

13. The blend of claim 12 wherein the monoester is formed from propylene glycol 1,2.

14. The blend of claim 12 wherein the monoester is formed from ethylene glycol.

15. The blend of claim 11 or 12 wherein the acid is ricinoleic acid.

16. The blend of claim 13 or 14 wherein the acid is ricinoleic acid.

17. The blend of claim 11 or 12 wherein the monoester is a blend of ethylene glycol monoricinoleate and propylene glycol monoricinoleate and wherein the acid in the multiester is ricinoleic acid.

18. The blend of claim 13 or 14 wherein the monoester is a blend of ethylene glycol monoricinoleate and propylene glycol monoricinoleate and wherein the acid in the multiester is ricinoleic acid.

19. The blend of claim 11 or 12 wherein the multiester is present as a component of castor oil and wherein the acid in the monoester is ricinoleic acid.

20. The blend of claim 13 or 14 wherein the multiester is present as a component of castor oil and wherein the acid in the monoester is ricinoleic acid.