A method for recycling poly(vinyl butyral) from multi-layer poly(vinyl butyral) sheets.

Abstract

A method for recovering stiff poly(vinyl butyral) from a plasticized poly(vinyl butyral) multi-layer sheet containing stiff poly(vinyl butyral) and soft poly(vinyl butyral) is disclosed. The method includes the steps of grinding the plasticized poly(vinyl butyral) multi-layer sheet to obtain granules, adding additional plasticizer to the granules to remove at least a portion of the soft poly(vinyl butyral), and physically separating the granules from the resulting solution.

Description

[Technical Field]

[0001]

[0001] The present disclosure relates to the field of recycling polymer interlayers for multilayer glass panels having at least one polymer interlayer sheet having a plurality of poly(vinyl butyral) components. [Background technology]

[0002]

[0002] Laminated safety glass used in automotive windshields and safety glass used in buildings are typically constructed from two laminated glass sheets with a plasticizing polymer interlayer in between. Poly(vinyl butyral) ("PVB") is generally the main component of the polymer interlayer.

[0003]

[0003] Poly(vinyl butyral) resin is typically mixed with a plasticizer before being melt-extruded into a sheet. Poly(vinyl butyral) resin and plasticizers are typically produced by a synthesis process that begins with the use of non-renewable raw materials. Poly(vinyl butyral) is obtained by the reaction of poly(vinyl alcohol) and butyraldehyde. The properties of poly(vinyl butyral) are determined by its molecular structure, residual hydroxyl group content, and residual acetate content, and the molecular structure is characterized by parameters such as its molecular weight and its distribution.

[0004]

[0004] In recent years, multilayer poly(vinyl butyral) interlayers for laminated glass have been sold to the market and are increasingly being used in laminated safety glass. Multilayer interlayers can provide enhanced sound insulation due to the presence of a softer layer ("core layer") in the center of the sheet. Typically, the core layer composition differs from the composition of the outer layer ("skin layer") in terms of the amount of plasticizer relative to the amount of polymer. The plasticizer content is typically higher in the core layer than in the skin layer. To allow for such differences in the interlayer composition, the PVB compound in the core layer has a different composition from the PVB compound in the skin layer in terms of hydroxyl group content or residual poly(vinyl acetate) content.

[0005]

[0005] Conventional multilayer interlayers, such as three-layer acoustic interlayers, include a soft core layer made of a single poly(vinyl butyral) ("PVB") resin having a low residual hydroxyl group content and a large amount of conventional plasticizer, and two rigid skin layers having a significantly higher residual hydroxyl group content (see, for example, U.S. Patents No. 5,340,654, 5,190,826, and 7,510,771). The opposite configuration, i.e., an interlayer having one rigid layer sandwiched between two more soft layers, has been found to improve the impact performance of glass panels and can also be designed for sound insulation.

[0006]

[0006] The following briefly describes how multilayer glass panels are generally produced in combination with these intermediate layers. First, at least one polymer intermediate layer sheet (single or multilayer) is placed between two substrates, and any excess intermediate layer is trimmed from the edges to create an assembly. It is not uncommon for multiple polymer intermediate layer sheets, or polymer intermediate layer sheets having multiple layers (or a combination of both), to be placed within two substrates to produce a multilayer glass panel having multiple polymer intermediate layers. Next, air is removed from the assembly by an applicable process or a method known to those skilled in the art, for example, by a nip roller, vacuum bag, or another degassing mechanism. In addition, the intermediate layers are partially pressed to the substrates by any method known to those skilled in the art. In the final step, to form the final unit structure, this preliminary bonding is made more permanent by a high-temperature, high-pressure lamination process, or any other method known to those skilled in the art, such as autoclave, but not limited to this.

[0007]

[0007] Cut portions or homogeneous poly(vinyl butyral) sheet products that do not meet quality standards can be reused in the sheet manufacturing process. After crushing, the chips or flakes can be added back to the feed material for the extrusion process. PVB raw materials can also be recovered from the laminated glass after it has served its purpose in its actual use. See U.S. Patent Application No. 2009 / 0209667. However, when such practices are applied to multilayer sheets, re-extrusion results in certain visual defects due to the presence of the core layer. Due to differences in the poly(vinyl butyral) composition between the PVB compounds in the skin and core layers, these materials do not mix well in the molten phase. This causes a certain type of visible haze in laminated glass containing PVB sheets where small pieces of the multilayer sheet are used during the raw material supply, resulting in products of inferior visual quality that are not suitable for market sale.

[0008]

[0008] Recycling poly(vinyl butyral) multilayer sheets from finished sheet products that do not meet quality standards and cannot be reused, and from laminated glass that has performed its primary function and is about to be discarded, can be an economic and environmental step forward. Recycling finished sheet products is less costly than producing brand new poly(vinyl butyral) resin, and moreover, it reduces the environmental footprint of poly(vinyl butyral) resin and sheet production. Therefore, maximizing scrap reuse is not only a competitive advantage but also an environmentally sound practice.

[0009]

[0009] U.S. Patent Application Publication No. 2003 / 0191202 discloses a method for separating a target polymer and its additives from a polymer-containing material, thereby enabling the recovery of both the target polymer and the additives. Based on the principle of selective precipitation, the target polymer is precipitated and subsequently separated from the additives and dissolved heterogenes present in the solution. Separation of the additives from the solution is carried out in a further step.

[0010]

[0010] U.S. Patent Application Publication US2009 / 0209667 discloses a method for recycling poly(vinyl butyral) resin and incorporating the poly(vinyl butyral) resin into laminated glass and other articles. The poly(vinyl butyral) resin is recovered from discarded laminated glass by a clearly defined process, which includes the steps of granulating the laminated glass, solvent extraction of plasticizers and impurities, dissolving the poly(vinyl butyral), pre-filtration of insoluble contaminants, color removal by adsorption or bleaching, post-filtration of carbon particles, precipitation of the poly(vinyl butyral), and washing, stabilizing, and drying the poly(vinyl butyral) resin. In one embodiment, the method is disclosed for separating two types of poly(vinyl butyral) resin from a single batch of granules. In this embodiment, a solvent is selected for the dissolution step that selectively dissolves the first poly(vinyl butyral) resin, rather than the second poly(vinyl butyral) resin, at a suitable temperature.

[0011]

[0011] There is still a need for methods to recycle PVB scrap material. [Overview of the project]

[0012]

[0012] In one embodiment, the present invention relates to a method for recovering rigid poly(vinyl butyral) from a plasticized poly(vinyl butyral) multilayer sheet containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral). According to one aspect of the present invention, the method comprises the step of crushing a plasticized poly(vinyl butyral) multilayer sheet to obtain poly(vinyl butyral) granules. Additional plasticizers may be added to these granules to remove at least a portion of the flexible poly(vinyl butyral) from the poly(vinyl butyral) granules so that the granules are rich in rigid poly(vinyl butyral). According to a further embodiment, the rigid poly(vinyl butyral) rich granules may be separated from the flexible poly(vinyl butyral) and additional plasticizers, leaving behind a varnish containing the flexible poly(vinyl butyral) and additional plasticizers, using one or more methods selected from, for example, decantation, filtration, or centrifugation.

[0013]

[0013] In one embodiment, the method of the present invention may further include one or more steps of adding an additional plasticizer to the granules to remove the additional portion of soft poly(vinyl butyral) from the granules, and then separating the granules from the additional portion of soft poly(vinyl butyral) and the additional plasticizer, leaving the additional portion of soft poly(vinyl butyral) and the additional plasticizer, using one or more methods selected from decantation, filtration, or centrifugation.

[0014]

[0014] According to a further aspect of the present invention, the resulting varnish is used to produce a poly(vinyl butyral) intermediate layer.

[0015]

[0015] Further aspects of the present invention are disclosed herein and claimed herein. [Modes for carrying out the invention]

[0016]

[0016] Accordingly, in one embodiment, the present invention relates to a method for recovering rigid poly(vinyl butyral) from a plasticized poly(vinyl butyral) multilayer sheet containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral). According to the present invention, the method may include the step of crushing the plasticized poly(vinyl butyral) multilayer sheet to obtain poly(vinyl butyral) granules. These granules may be in the form of flakes or chips, etc., without being limited in any way.

[0017]

[0017] The present invention may further include adding an additional plasticizer to poly(vinyl butyral) granules to wash or remove at least a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules so that the granules become rich in rigid poly(vinyl butyral). Thus, the rigid poly(vinyl butyral)-rich granules become solid, facilitating the separation of the granules from the resulting soft poly(vinyl butyral) and additional plasticizer. Accordingly, the present invention also includes separating the rigid poly(vinyl butyral)-rich granules from the soft poly(vinyl butyral) and additional plasticizer, as described herein as varnish, using one or more methods selected from, for example, decantation, filtration, or centrifugation.

[0018]

[0018] In a further embodiment, the present invention may further include one or more additional steps of adding further additional plasticizers to the granules to remove additional portions of soft poly(vinyl butyral) from the granules, and then separating the granules from the additional portions of soft poly(vinyl butyral) and the further additional plasticizer varnish using one or more methods selected from decantation, filtration, or centrifugation. In each of the steps according to the present invention, the additional plasticizer used may be the same as or different from the plasticizer present in the plasticized poly(vinyl butyral) multilayer sheet.

[0019]

[0019] Accordingly, as used herein, the term “varnish” is used to describe the resulting soft poly(vinyl butyral) and additional plasticizers when the granular material is enriched with rigid poly(vinyl butyral) granular material by the use of plasticizers.

[0020]

[0020] Surprisingly, we discovered that by using plasticizers, such as those typically used to make PVB plastic, it is possible to selectively wash away some of the soft poly(vinyl butyral) from a granular poly(vinyl butyral) mixture, and obtain granules that are rich in rigid poly(vinyl butyral), and varnishes that can be used to produce poly(vinyl butyral) intermediate layers.

[0021]

[0021] In one embodiment, according to any of the preceding embodiments, the flexible poly(vinyl butyral) may have a residual hydroxyl group content of about 8% to about 12%. In yet another embodiment, the rigid poly(vinyl butyral) may have a residual hydroxyl group content of about 15% to about 25%.

[0022]

[0022] In a further embodiment, according to any of the preceding embodiments, the plasticized poly(vinyl butyral) multilayer sheet may contain triethylene glycol bis(2-ethylhexanoate) present as a plasticizer.

[0023]

[0023] In yet another embodiment, according to any of the preceding embodiments, the plasticized poly(vinyl butyral) multilayer sheet may further contain another convenient substance present as a plasticizer, such as dihexyl adipate, or bis(2-ethylhexyl)adipate, or benzoflex 9-88 benzoate ester.

[0024]

[0024] In another aspect, according to any of the preceding aspects, the additional plasticizer is selected from one or more of esters of polybasic acids or polyhydric alcohols. In a further aspect, the additional plasticizer may be selected from one or more of triethylene glycol bis(2-ethylhexanoate), tetraethylene glycol bis(2-ethylhexanoate), triethylene glycol bis(2-ethylbutyrate), triethylene glycol diheptanoate, tetraethylene glycol diheptanoate, dihexyl adipate, bis(2-ethylhexyl) adipate, bis(2-ethoxyethyl) adipate, dioctyl adipate, hexyl cyclohexyl adipate, diisononyl adipate, heptyl nonyl adipate, dibutyl sebacate, adipic acid polymer, soybean oil, or epoxidized soybean oil.

[0025]

[0025] In one aspect, according to any of the preceding aspects, triethylene glycol bis(2-ethylhexanoate) is present in the flexible poly(vinyl butyral) in an amount of about 60 phr to about 100 phr. In another aspect, the additional plasticizer added to the poly(vinyl butyral) granules in step b) comprises triethylene glycol bis(2-ethylhexanoate).

[0026]

[0026] In a further aspect, according to any of the preceding aspects, the difference between the residual hydroxyl group content of the flexible poly(vinyl butyral) and the residual hydroxyl group content of the rigid poly(vinyl butyral) is at least 4.0 weight percent.

[0027]

[0027] In yet another aspect, according to any of the preceding aspects, the rigid poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet comprises about 30 phr to about 45 phr of a plasticizer.

[0028]

[0028] In one embodiment, according to any of the preceding embodiments, the flexible poly(vinyl butyral) may be isolated from the mixture of the flexible poly(vinyl butyral) and additional plasticizer obtained from step b) by one or more of the following methods for isolating the flexible poly(vinyl butyral): sedimentation, filtration, centrifugation, evaporation, or precipitation. In another embodiment, the present invention relates to a poly(vinyl butyral) sheet containing the isolated flexible poly(vinyl butyral), and laminated glass containing this poly(vinyl butyral) sheet.

[0029]

[0029] In a further embodiment, according to any of the preceding embodiments, the resulting varnish of flexible poly(vinyl butyral) and plasticizer may be used directly, with the optional removal of water, without first isolating the flexible poly(vinyl butyral) from the plasticizer, to produce a varnish-containing poly(vinyl butyral) sheet or intermediate layer.

[0030]

[0030] In yet another embodiment, according to any of the preceding embodiments, the present invention relates to poly(vinyl butyral) sheets containing separated, rigid poly(vinyl butyral)-rich granules recovered according to the method of the present invention. In yet another embodiment, the present invention relates to laminated glass containing these poly(vinyl butyral) sheets containing rigid poly(vinyl butyral)-rich granules.

[0031]

[0031] In yet another embodiment, according to any of the preceding embodiments, the method may further include the step of isolating the flexible poly(vinyl butyral) and the varnish of an additional plasticizer by subjecting them to one or more of the following: sedimentation, filtration, centrifugation, evaporation, or precipitation.

[0032]

[0032] In further embodiments, according to any of the preceding embodiments, the method may further include the step of adding a varnish of flexible poly(vinyl butyral) and additional plasticizers to the poly(vinyl butyral) composition.

[0033]

[0033] In further embodiments, according to any of the preceding embodiments, the method may further include the step of forming the poly(vinyl butyral) composition into a sheet.

[0034]

[0034] In another embodiment, according to any of the preceding embodiments, the method may further include the step of adding a varnish of flexible poly(vinyl butyral) and an additional plasticizer to a poly(vinyl butyral) composition containing a whitening agent to form a translucent intermediate layer.

[0035]

[0035] In yet another embodiment, according to any of the preceding embodiments, the method may further include the step of adding a varnish of flexible poly(vinyl butyral) and additional plasticizers to a transparent poly(vinyl butyral) compound.

[0036]

[0036] In yet another embodiment, or in any of the preceding embodiments, the present invention relates to a poly(vinyl butyral) sheet containing isolated flexible poly(vinyl butyral) according to any of the preceding embodiments, and in yet another embodiment, the present invention relates to laminated glass containing a poly(vinyl butyral) sheet according to any of the preceding embodiments.

[0037]

[0037] In yet another embodiment, according to any of the preceding embodiments, the present invention may relate to a poly(vinyl butyral) sheet comprising separated, rigid poly(vinyl butyral)-rich granules according to any of the preceding embodiments.

[0038]

[0038] In yet another embodiment, according to any of the preceding embodiments, the present invention may relate to laminated glass comprising a poly(vinyl butyral) sheet of any of the preceding embodiments.

[0039]

[0039] The term “rigid poly(vinyl butyral)” refers to a poly(vinyl butyral) resin or a blend of poly(vinyl butyral) resins that is significantly more rigid than “flexible poly(vinyl butyral)” and typically forms the skin or rigid layer of a multilayer poly(vinyl butyral) sheet, as further described herein.

[0040]

[0040] The term “flexible poly(vinyl butyral)” refers to a poly(vinyl butyral) resin or blend of poly(vinyl butyral) resins that is significantly more flexible than “rigid poly(vinyl butyral)” and typically forms the core or flexible layer of a multilayer poly(vinyl butyral) sheet, as further described herein. The flexible or core poly(vinyl butyral) layer is typically sandwiched between two rigid or skin poly(vinyl butyral) layers to form a multilayer poly(vinyl butyral) sheet.

[0041]

[0041] As used herein, the term “plasticizer” generally refers to molecules or blends of molecules that make a polymer, specifically poly(vinyl butyral), plastic and thereby soften it, at a low plasticizer content, as further described herein. Furthermore, according to the present invention, plasticizers useful as additional plasticizers, when present in larger quantities as additional plasticizers, help to remove soft poly(vinyl butyral) from granular poly(vinyl butyral) mixtures by selectively washing or partially dissolving the soft poly(vinyl butyral), which is due in part to the higher affinity or compatibility of the core layer to the plasticizer, as can be seen from its low residual hydroxyl group content.

[0042]

[0042] In some embodiments, the additional plasticizer has hydrocarbon segments with fewer than 20, 15, 12, or 10 carbon atoms. Suitable additional plasticizers for use according to the present invention include, among many, esters of polybasic acids or polyhydric alcohols. Suitable plasticizers include, for example, triethylene glycol bis(2-ethylhexanoate) ("3-GEH"), tetraethylene glycol bis(2-ethylhexanoate), triethylene glycol bis(2-ethylbutyrate), triethylene glycol diheptanoate, tetraethylene glycol diheptanoate, dihexyl adipate, bis(2-ethylhexyl) adipate, dioctyl adipate, hexylcyclohexyl adipate, diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, adipate polymers, soybean oil, and epoxidized soybean oil, and mixtures thereof. A more preferred plasticizer is 3-GEH. In addition, plasticizers that are suitable at high temperatures may be preferred to further increase the fluidity of the intermediate layer.

[0043]

[0043] As used herein, the term “poly(vinyl butyral) multilayer sheet” refers to a sheet composed of various layers of poly(vinyl butyral) resin, the various layers being typically flexible or core layers having rigid or skin layers on each side of the core layer. Accordingly, the poly(vinyl butyral) multilayer sheet of the present invention comprises at least one flexible poly(vinyl butyral) and at least one rigid poly(vinyl butyral).

[0044]

[0044] When we say that a poly(vinyl butyral) multilayer sheet is crushed to obtain a granular poly(vinyl butyral) mixture, it means that the size is reduced by any suitable means for obtaining granules, chips, or flakes, etc. (all of which may be considered granules according to the present invention), for example, by a crusher. In this granulation step, granulation can be carried out using any suitable apparatus, which may be a commercially available granulator such as a Granutec granulator (East Douglas, Mass., USA). The scrap is granulated to reduce its particle size. Granulation of scrap can result in individual granules having a length of less than 2.6 centimeters, or 0.1 to 1.0 centimeters, or 0.4 to 0.8 centimeters. While granules with a size greater than 2.6 centimeters can be used, it is generally desirable to granulate the sheet to smaller sizes, which results in a larger total surface area of ​​granules. At any point during the granulation process, the granulated flakes can be sieved to remove contaminants released from the poly(vinyl butyral).

[0045]

[0045] When it is said that the additional plasticizer is added to the poly(vinyl butyral) granules, it means that the plasticizer added in this step is added to the plasticizer contained in the plasticized poly(vinyl butyral) multilayer sheet. In fact, both flexible poly(vinyl butyral) and rigid poly(vinyl butyral) will already contain plasticizers. The additional plasticizer may be the same plasticizer present in the flexible poly(vinyl butyral) and / or rigid poly(vinyl butyral), or it may be different from the plasticizer present in the flexible poly(vinyl butyral) and / or rigid poly(vinyl butyral). The amount of additional plasticizer added is sufficient to help remove or wash away at least some of the flexible poly(vinyl butyral) from the poly(vinyl butyral) granules to obtain a varnish of flexible poly(vinyl butyral) and plasticizer.

[0046]

[0046] When it is said that at least a portion of the soft poly(vinyl butyral) is removed from the poly(vinyl butyral) granules, it means that a portion of the soft poly(vinyl butyral) is washed or dissolved from the granules. The granules may then be separated from the soft poly(vinyl butyral) and additional plasticizers according to one or more of the following methods further described herein: decantation, filtration, or centrifugation. Alternatively, the varnish may be used directly to form a poly(vinyl butyral) layer or sheet, or optionally, a portion of the additional plasticizers and / or water may be separated from the varnish prior to the formation of a poly(vinyl butyral) sheet or layer from the varnish.

[0047]

[0047] When it is said that the granular material is rich in rigid poly(vinyl butyral), it means that the relative amount of rigid poly(vinyl butyral) in the granular material is higher than before some of the soft poly(vinyl butyral) was washed away from the granular material.

[0048]

[0048] In one embodiment, a flexible or core poly(vinyl butyral), or a blend of flexible poly(vinyl butyral), may have a residual hydroxyl group content of about 5% to about 15%, as further described herein. Alternatively, the residual hydroxyl group content of the core poly(vinyl butyral) may be about 7% to about 13%, or 8% to 12%, or as further described herein.

[0049]

[0049] In one embodiment, a flexible or core poly(vinyl butyral), or a blend of flexible poly(vinyl butyral), may have a residual acetate content of about 0% to about 18%, as further described herein. Alternatively, the residual acetate content may be less than 10%, or less than 5%, or less than 2%, or less than 1%, or as further described herein.

[0050]

[0050] The amount of plasticizer in the flexible or core poly(vinyl butyral), or the blend of flexible poly(vinyl butyral), may be about 50 phr to about 150 phr, or 55 phr to 120 phr, or 60 to 100 phr.

[0051]

[0051] In another embodiment, rigid poly(vinyl butyral) or a blend of rigid poly(vinyl butyral) may have a residual hydroxyl group content of about 12% to about 28%, as further described herein. Alternatively, the residual hydroxyl group content of rigid poly(vinyl butyral) may be about 15% to about 25%, or 18% to 20%, or as further described herein.

[0052]

[0052] In another embodiment, rigid poly(vinyl butyral) or a blend of rigid poly(vinyl butyral) may have a residual acetate content of about 0% to about 18%, as further described herein. Alternatively, the residual acetate content of rigid poly(vinyl butyral) may be less than 10%, or less than 5%, or less than 2%, or less than 1%, or as further described herein.

[0053]

[0053] In another embodiment, the residual hydroxyl group content of the core layer may be the same as, greater than, or less than the residual hydroxyl group content of the resin in the skin layer. In various embodiments, the core resin, or the skin resin, or both thereof, may be calculated as a polyvinyl ester, for example, an acetate, and may contain less than 30 wt.% of residual ester groups, less than 25 wt.% of residual ester groups, less than 20 wt.% of residual ester groups, less than 15 wt.% of residual ester groups, less than 13 wt.% of residual ester groups, less than 10 wt.% of residual ester groups, less than 7 wt.% of residual ester groups, less than 5 wt.% of residual ester groups, and the remainder being an acetal such as butyraldehyde acetal, but optionally, isobutyraldehyde acetal group, 2-ethylhexanal acetal group, or any mixture of any two of butyraldehyde acetal, isobutyraldehyde acetal, and 2-ethylhexanal acetal groups, or other acetal groups such as those discussed elsewhere in this specification.

[0054]

[0054] In one embodiment, the multilayer intermediate layer may include a first skin polymer layer containing plasticized poly(vinyl butyral) having a molecular weight of less than about 140,000 daltons, a second core polymer layer containing plasticized poly(vinyl butyral) having a molecular weight of more than about 140,000 daltons, and a third skin polymer layer containing plasticized poly(vinyl butyral) having a molecular weight of less than about 140,000 daltons. The second polymer layer is positioned between the first polymer layer and the third polymer layer and forms two skin layers and a central core layer.

[0055]

[0055] In various embodiments of the intermediate layer of this disclosure, the intermediate layer may contain about 30 to about 60 phr (parts per 100 parts of resin) of total plasticizer. While the total plasticizer content is shown above, the plasticizer content in the skin layer or core layer may differ from the total plasticizer content. In addition, the skin layer and core layer may have different plasticizer content, since the plasticizer content of each layer in equilibrium is at least partially determined by its respective residual hydroxyl group content. For example, in equilibrium, if the combined thickness of the skin layer is equal to that of the core layer, for a total plasticizer amount of about 54.3 phr of intermediate layer, the intermediate layer may consist of two skin layers, each having 38 phr of plasticizer, and a core layer having 75 phr of plasticizer. With respect to thicker or thinner skin layers, the total plasticizer amount for the intermediate layer may vary accordingly.

[0056]

[0056] In other embodiments, the amount of plasticizer in the blend of rigid or skin poly(vinyl butyral) or flexible poly(vinyl butyral) may be about 20 phr to about 60 phr, or 25 phr to 50 phr, or 30 to 45 phr.

[0057]

[0057] In further embodiments, the difference between the residual hydroxyl group content of the flexible poly(vinyl butyral) and the residual hydroxyl group content of the rigid poly(vinyl butyral) is at least 6%, or at least 5%, or at least 4%, or 4% to 8%, or 5% to 10%, or as further described herein.

[0058]

[0058] Accordingly, in various embodiments, the residual hydroxyl group content of the poly(vinyl butyral) resin for the skin layer and core layer may differ. The resin for the core layer may contain, for example, about 9 to about 18 wt.% of residual hydroxyl groups calculated as PVOH, about 9 to about 16 wt.% of residual hydroxyl groups calculated as PVOH, or about 9 to about 14 wt.% of residual hydroxyl groups calculated as PVOH. The resin for the skin layer may contain, for example, about 13 to about 35 wt.% of residual hydroxyl groups calculated as PVOH, about 13 to about 30 wt.% of residual hydroxyl groups calculated as PVOH, or about 15 to about 22 wt.% of residual hydroxyl groups calculated as PVOH, and, with respect to a particular embodiment, about 17.25 to about 22.25 wt. of residual hydroxyl groups calculated as PVOH, or as described elsewhere in this specification. The resin for the core layer, or for the skin layer, or for both the skin and core layers, is calculated as a polyvinyl ester, for example, an acetate, and may also contain less than 20 wt.% of residual ester groups, less than 15 wt.%, less than 13 wt.%, less than 11 wt.%, less than 9 wt.%, less than 7 wt.%, less than 5 wt.%, or less than 1 wt.%, with the remainder being an acetal, preferably a butyraldehyde acetal, but optionally containing small amounts of other acetal groups, for example, a 2-ethylhexanal group (see, for example, U.S. Patent No. 5,137,954, the entire disclosure of which is cited herein by reference).

[0059]

[0059] In one embodiment, flexible poly(vinyl butyral), rigid poly(vinyl butyral), and / or plasticized poly(vinyl butyral) multilayer sheets, or any other poly(vinyl butyral) described herein, include dipropylene glycol dibenzoate, tripylene glycol dibenzoate, polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexyl benzoate, diethylene glycol benzoate, butoxyethyl benzoate, butoxyethoxyethyl benzoate, butoxyethoxyethoxyethyl benzoate, propylene glycol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol dibenzoate The plasticizer may be selected from one or more of the following: 2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanediol dibenzoate, diethylene glycol di-o-toluate, triethylene glycol di-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate, tri-2-ethylhexyl trimelitate, di-2-ethylhexyl terephthalate, bis-phenol A bis(2-ethylhexaonate), di-(butoxyethyl)terephthalate, di-(butoxyethioxyethyl)terephthalate, bis(2-ethoxyethyl)azipart, or any other plasticizer further described herein.

[0060]

[0060] In various embodiments, additional plasticizers that may be added include dipropylene glycol dibenzoate, tripropylene glycol dibenzoate, polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexyl benzoate, diethylene glycol benzoate, butoxyethyl benzoate, butoxyethoxyethyl benzoate, butoxyethoxyethoxyethyl benzoate, propylene glycol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanediol di The plasticizer may include one or more of the following: benzoate, diethylene glycol di-o-toluate, triethylene glycol di-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate, tri-2-ethylhexyl trimelitate, di-2-ethylhexyl terephthalate, bisphenol A bis(2-ethylhexaonate), di-(butoxyethyl) terephthalate, di-(butoxyethyl) terephthalate, or any of the others further described herein, which may be the same as or different from the plasticizers in the poly(vinyl butyral) described herein, as further described herein. Additional plasticizers or further plasticizers suitable as plasticizers in flexible poly(vinyl butyral) are described elsewhere in this specification.

[0061]

[0061] As described above, the poly(vinyl butyral) multilayer sheet of the present invention typically includes a rigid poly(vinyl butyral) layer and a flexible poly(vinyl butyral) layer. As described above, the core layer typically includes flexible poly(vinyl butyral) sandwiched between rigid poly(vinyl butyral) skin layers to form the poly(vinyl butyral) multilayer sheet of the present invention.

[0062]

[0062] In one embodiment, the amount of additional plasticizer added to the poly(vinyl butyral) granules is sufficient to wash, extract, or selectively dissolve a portion of the soft poly(vinyl butyral).

[0063]

[0063] In another embodiment, the amount of additional plasticizer added to the poly(vinylbutyral) granules is sufficient to suspend the rigid poly(vinylbutyral) granules of the mixture and thus form a rigid poly(vinylbutyral) suspension.

[0064]

[0064] In yet another embodiment, the additional plasticizer is added to the poly(vinyl butyral) granules in a continuous process to form, for example, a countercurrent process, which removes at least a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules so that the granules are rich in stiff poly(vinyl butyral). The granules may then be separated from the resulting varnish mixture of soft poly(vinyl butyral) and the additional plasticizer, or the varnish may be used without separating the additional plasticizer from the soft poly(vinyl butyral), or with only the additional plasticizer partially separated from the soft poly(vinyl butyral), or with only the water separated from the mixture.

[0065]

[0065] In a further embodiment of the present invention, the method may include, after the step of physical separation, a further step of isolating the flexible poly(vinyl butyral) from the resulting mixture of the flexible poly(vinyl butyral) and an additional plasticizer by subjecting it to one or more of the following: sedimentation, filtration, centrifugation, evaporation, or precipitation.

[0066]

[0066] In a further embodiment, the present invention relates to poly(vinyl butyral) sheets comprising isolated rigid poly(vinyl butyral), and laminated glass comprising these poly(vinyl butyral) sheets.

[0067]

[0067] In a further embodiment, the present invention relates to poly(vinyl butyral) sheets containing flexible poly(vinyl butyral), and laminated glass containing these poly(vinyl butyral) sheets, regardless of whether the flexible poly(vinyl butyral) is initially isolated from the plasticizer.

[0068]

[0068] When it is said that rigid poly(vinyl butyral) is separated from a poly(vinyl butyral) mixture by decantation or sedimentation, it means, for example, that the liquid is separated from the rigid poly(vinyl butyral) solid by allowing the solid to settle to the bottom of the container and removing the bulk of additional plasticizer from the granular material.

[0069]

[0069] When it is said that rigid poly(vinyl butyral) is separated by filtration, it means that the solid granular rigid poly(vinyl butyral) is filtered out of the plasticizer.

[0070]

[0070] When it is said that rigid poly(vinyl butyral) is separated from a mixture by centrifugal separation, it means that the solid is separated from the liquid using a centrifuge.

[0071]

[0071] The present invention may be further understood by following further description.

[0072]

[0072] Accordingly, in one embodiment, the multilayer poly(vinyl butyral) sheet of the present invention may include an intermediate layer comprising one or more rigid skin layers and a flexible core layer. In one embodiment, these multilayer intermediate layer sheets may include a first polymer layer (skin layer) comprising a rigid plasticized poly(vinyl butyral) resin, a second polymer layer (core layer) comprising a flexible plasticized poly(vinyl butyral) resin, or a blend thereof having the same or different residual hydroxyl group content, and optionally a third polymer layer (skin layer) comprising a rigid plasticized poly(vinyl butyral) resin. The second or core polymer layer is positioned adjacent to the first polymer layer. If there are three or more layers, the second polymer layer may be positioned between the first polymer layer and the third polymer layer, forming two skin layers and a central core layer.

[0073]

[0073] In embodiments, the second or core poly(vinyl butyral) resin may be present in an amount of about 2% to about 45% by weight, or about 5% to about 40% by weight.

[0074]

[0074] Plasticizers work by being embedded between polymer chains, increasing the spacing between them ("free volume"), and therefore significantly lowering the glass transition temperature (Tg) of the polymer resin (typically only 0.5-4 degrees Celsius / phr), making the material softer. In this regard, the amount of plasticizer in the interlayer can be adjusted to affect the glass transition temperature (Tg). The glass transition temperature (Tg) is the temperature at which the interlayer transitions from a glassy state to a rubbery state. Generally, the more plasticizer added, the lower the Tg. Conventional interlayers have generally had Tgs ranging from about 0°C for acoustic (noise suppression) interlayers to about 45°C for hurricane and aircraft interlayer applications.

[0075]

[0075] The glass transition temperature of the interlayer also correlates with the stiffness of the interlayer, with higher glass transition temperatures resulting in stiffer interlayers. Generally, interlayers with a glass transition temperature of about 30°C or higher increase the strength and torsional stiffness of the windshield. On the other hand, softer interlayers (generally characterized by interlayers with a glass transition temperature of less than about 30°C) contribute to sound attenuation effects (i.e., acoustic properties). The multilayer interlayers of this disclosure are harder or stiffer skin layers (e.g., stiff / / soft / / stiff) laminated with a softer core layer, combining these two advantageous properties (i.e., strength and acoustics) by utilizing a skin layer with increased fluidity at autoclave temperatures. In various embodiments, the multilayer interlayers generally include a skin layer having a glass transition temperature of about 30°C to about 55°C, and a core layer having a glass transition temperature of about 0°C to about 10°C.

[0076]

[0076] In embodiments, the plasticizers used herein are dipropylene glycol dibenzoate, tripylene glycol dibenzoate, polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexyl benzoate, diethylene glycol benzoate, butoxyethyl benzoate, butoxyethoxyethyl benzoate, butoxyethoxyethoxyethyl benzoate, propylene glycol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol The plasticizer may be selected from benzoate isobutyrate, 1,3-butanediol dibenzoate, diethylene glycol di-o-toluate, triethylene glycol di-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate, tri-2-ethylhexyl trimelitate, di-2-ethylhexyl terephthalate, bisphenol A bis(2-ethylhexaonate), di-(butoxyethyl)terephthalate, di-(butoxyethyl)terephthalate, and mixtures thereof, or as described elsewhere in this specification. In embodiments, the plasticizer may be a mixture of two or more plasticizers. In embodiments, the intermediate layer may further contain a second high refractive index plasticizer having a refractive index of at least 1.460. In other embodiments, the intermediate layer may further contain a plasticizer having a refractive index of less than about 1.450.

[0077]

[0077] In embodiments, the percent haze may be less than 0.5% (measured using Illuminant C at a 2-degree observation angle and according to ASTM D1003-61 (Re-approved 1977)-Procedure A).

[0078]

[0078] In embodiments, the residual hydroxyl group content of the third or rigid poly(vinyl butyral resin) is typically the same as that of the first rigid poly(vinyl butyral resin), and typically different from that of the second or core poly(vinyl butyral resin). In embodiments, the difference between the core residual hydroxyl group content and the skin residual hydroxyl group content is at least 4.0 weight percent, or at least 6.0 weight percent.

[0079]

[0079] In the embodiment, the second poly(vinyl butyral) resin is present in an amount of about 2% to about 45% by weight, or about 5% to about 40% by weight.

[0080]

[0080] In one embodiment, the polymer intermediate layer has at least two different glass transition temperatures (T g ) has at least two different glass transition temperatures (T g The difference between them is at least 5°C.

[0081]

[0081] In the embodiment, the residual hydroxyl group content of the third or skin poly(vinyl butyral resin) is the same as the residual hydroxyl group content of the first or core poly(vinyl butyral) resin.

[0082]

[0082] Multilayer panels are also disclosed. A multilayer panel comprises at least one rigid substrate and a polymer intermediate or multilayer polymer intermediate as disclosed herein. The panel has improved optical properties.

[0083]

[0083] In one embodiment of the present invention, a single plasticizer such as triethylene glycol bis(2-ethylhexanoate) or a mixture thereof with dihexyl adipate may be used.

[0084]

[0084] Accordingly, the present invention relates to a method for preferentially removing, washing, or partially dissolving flexible poly(vinyl butyral) resin from poly(vinyl butyral) granular material by using a plasticizer as an extractant and taking advantage of the differences in the solubility of PVB components in the plasticizer. This is distinct from the use of traditional solvents. Accordingly, the present invention optionally provides a method for recovering raw materials for reintroduction into the manufacturing process without first isolating the flexible poly(vinyl butyral) resin from the plasticizer.

[0085]

[0085] Due to differences in the cloud points of PVB resins of different compositions, specifically measured by residual %PVOH in the plasticizer, the method allows for the use of temperature as an important parameter for the effective separation of different PVB components. In this regard, additional plasticizers may be added to poly(vinyl butyral) granules at temperatures of at least 25°C, or at least 30°C, or about 25°C to about 90°C, or 30°C to about 60°C, or as otherwise disclosed herein.

[0086]

[0086] The present invention also describes a method for removing the extracted PVB resin from the plasticizer extract to enable repeated use of the plasticizer in the recycling process.

[0087]

[0087] Accordingly, the present invention describes a method for removing extracted poly(vinyl butyral) from plasticizers to enable repeated use of the solvent in the extraction. Poly(vinyl butyral) compounds isolated from multilayer poly(vinyl butyral) sheets with a purity acceptable for reuse are the result of a method comprising the steps described in the present invention as fractionation, extraction, or selective dissolution. In this context, fractionation, extraction, or selective dissolution mainly means that flexible poly(vinyl butyral) is removed or washed from poly(vinyl butyral) granules, while rigid poly(vinyl butyral) resin remains as a solid in the solvent, mainly in the poly(vinyl butyral) granules, and sometimes in a swollen state.

[0088]

[0088] Poly(vinylbutyral) compounds are components of multilayer poly(vinylbutyral) sheets, where each layer consists of poly(vinylbutyral) and plasticizers having different compositions with respect to the poly(vinylbutyral) composition, namely different residual hydroxyl group or residual acetate content and plasticizer content. Generally, the amount of plasticizer relative to the amount of poly(vinylbutyral) is different. Significant extraction of poly(vinylbutyral) compounds from multilayer sheet granules is typically obtained after grinding sheets below quality standards into smaller flakes, generally in the range of 3 to 30 mm in size.

[0089]

[0089] The degree of separation depends on the plasticizer applied. For example, when extracting the core layer PVB from a poly(vinyl butyral) multilayer sheet using triethylene glycol bis(2-ethylhexanoate), the process proceeds to the extent that 25-50% of the core layer PVB is removed in a single fractionation step. Repeating the extraction will increase the degree of separation between different poly(vinyl butyral) compounds. Typically, the extraction is achieved when the multilayer sheet or its components are exposed to a specific solvent in a temperature range between 25-100°C, and the extraction time for one extraction cycle is between 5 minutes and several days.

[0090]

[0090] Conventional multilayer interlayers, such as three-layer acoustic interlayers, typically contain a flexible core layer made of a single poly(vinyl butyral) ("PVB") resin having a low residual hydroxyl group content and a large amount of conventional plasticizer, and two rigid skin layers having a significantly higher residual hydroxyl group content (see, for example, U.S. Patents 5,340,654, 5,190,826, and 7,510,771). Therefore, isolated flexible poly(vinyl butyral) may be recycled to form the core layer of the three-layer acoustic interlayer, or a varnish of flexible poly(vinyl butyral) and plasticizer may be used directly without first separating the two to form the flexible poly(vinyl butyral) layer. The residual hydroxyl group content and the amount of plasticizer in the PVB core resin are optimized so that the interlayer provides optimal sound insulation properties for multilayer glass panels such as windshields and windows installed in vehicles and buildings under ambient conditions.

[0091]

[0091] The terms “polymer intermediate sheet,” “intermediate layer,” and “polymer melt sheet” as used herein may generally refer to a single-layer sheet or a multilayer intermediate sheet. A “single-layer sheet,” as its name suggests, is a single polymer layer extruded as a single layer. On the other hand, a multilayer intermediate sheet may include multiple layers, including separately extruded layers, co-extruded layers, or any combination of separately extruded layers and co-extruded layers. Thus, a multilayer intermediate sheet may include, for example, two or more combined single-layer sheets ("multi-layer sheets"), two or more layers co-extruded together ("co-extruded sheets"), two or more combined co-extruded sheets, a combination of at least one single-layer sheet and at least one co-extruded sheet, a combination of a single-layer sheet and a multi-layer sheet, and a combination of at least one multi-layer sheet and at least one co-extruded sheet. In various embodiments of this disclosure, a multilayer intermediate sheet comprises at least two polymer layers (e.g., co-extruded and / or laminated single or multiple layers) arranged in direct contact with one another, where each layer comprises a polymer resin, as will be more fully described below. As used herein for multilayer intermediates having at least three layers, “skin layer” generally refers to the outer layer of the intermediate, and “core layer” generally refers to the inner layer. Thus, one exemplary embodiment would be skin layer / / core layer / / skin layer.

[0092]

[0092] PVB resins are produced by known acetalization processes, which involve reacting polyvinyl alcohol ("PVOH") with butyraldehyde in the presence of an acid catalyst, followed by separation, stabilization, and drying of the resin. Such acetalization processes are disclosed, for example, in U.S. Patents 2,282,057 and 2,282,026, and in Vinyl Acetal Polymers, in Encyclopedia of Polymer Science & Technology, 3rd edition, Volume 8, pp. 381-399 (2003) by BEWade, the entirety of which is incorporated herein by reference. The resins are commercially available in various forms, for example, as Butvar® resin from Solutia Inc., a wholly owned subsidiary of Eastman Chemical Company.

[0093]

[0093] As used herein, the residual hydroxyl group content in PVB (calculated by weight as % vinyl alcohol or % PVOH) refers to the amount of hydroxyl groups remaining on the polymer chain after the process is complete. For example, PVB can be produced by hydrolyzing poly(vinyl acetate) to poly(vinyl alcohol (PVOH)), and then reacting the PVOH with butyraldehyde. In the process of hydrolyzing poly(vinyl acetate), typically not all acetate side groups are converted to hydroxyl groups. Furthermore, the reaction with butyraldehyde typically does not result in all hydroxyl groups being converted to acetal groups. As a result, in any final PVB resin, typically residual acetate groups (as vinyl acetate groups) and residual hydroxyl groups (as vinyl hydroxyl groups) will be present as side groups on the polymer chain. As used herein, the residual hydroxyl group content and residual acetate content are measured in weight percent (wt.%) in accordance with ASTM D1396.

[0094]

[0094] The PVB resins of this disclosure typically have a molecular weight greater than 50,000 daltons, less than 500,000 daltons, or about 50,000 to about 500,000 daltons, or about 70,000 to about 500,000 daltons, or about 100,000 to about 425,000 daltons, as measured by size exclusion chromatography using low-angle laser light scattering. As used herein, the term "molecular weight" means weight-average molecular weight.

[0095]

[0095] Various adhesion control agents ("ACAs") can be used in the intermediate layers of the present disclosure to control the adhesion of the intermediate layer sheet to the glass. In various embodiments of the intermediate layers of the present disclosure, the intermediate layer may contain about 0.003 to about 0.15 parts ACA per 100 parts of resin, about 0.01 to about 0.10 parts ACA per 100 parts of resin, and about 0.01 to about 0.04 parts ACA per 100 parts of resin. Such ACAs include, but are not limited to, the ACA disclosed in U.S. Patent No. 5,728,472 (the entire disclosure is cited herein by reference), sodium residual acetate, potassium acetate, magnesium bis(2-ethyl butyrate), and / or magnesium bis(2-ethylhexanoate).

[0096]

[0096] Other additives may be added to the intermediate to enhance its performance in the final product and impart certain additional properties to the intermediate. Such additives include, but are not limited to, dyes, pigments, stabilizers (e.g., UV stabilizers), antioxidants, antiblocking agents, flame retardants, IR absorbers or blockers (e.g., indium tin oxide, antimony tin oxide, lanthanum hexaboride (LaB6), and tungsten cesium oxide), processing aids, flow-promoting additives, lubricants, impact modifiers, nucleating agents, thermal stabilizers, UV absorbers, dispersants, surfactants, chelating agents, coupling agents, adhesives, primers, reinforcing additives, and fillers, among other additives known to those skilled in the art.

[0097]

[0097] The plasticizer or mixture of plasticizers in the skin and core layers is selected so that the multilayer acoustic interlayer exhibits acceptable levels of haze and visible transmittance. In various embodiments, the plasticizer is selected from a high refractive index plasticizer, a mixture of two or more high refractive index plasticizers, or a mixture of a conventional plasticizer and a high refractive index plasticizer. In various embodiments, the high refractive index plasticizer is selected to eliminate the strong haze that may occur from blending two or more resins with different residual hydroxyl group content. In various embodiments of this disclosure, the haze is less than 5%, less than 3%, and less than 1%, less than 0.3%.

[0098]

[0098] As used herein, plasticizers having a refractive index of about 1.450 or less are referred to as “conventional plasticizers”. Conventional plasticizers include, but are not limited to, triethylene glycol bis(2-ethylhexanoate) ("3-GEH"), triethylene glycol bis(2-ethylbutyrate), triethylene glycol diheptanoate, tetraethylene glycol diheptanoate, tetraethylene glycol bis(2-ethylhexanoate), dihexyl adipate, dioctyl adipate, hexylcyclohexyl adipate, diisononyl adipate, heptylnonyl adipate, di(butoxyethyl)adipate, bis(2-butoxyethyl)adipate, and bis(2-(2-butoxyethoxy)ethyl)adipate, dibutyl sebacate, dioctyl sebacate, and mixtures thereof. These plasticizers have a refractive index of approximately 1.442 to 1.449. For comparison, PVB resin has a refractive index of approximately 1.485 to 1.495. 3-GEH (refractive index = 1.442) is the most common plasticizer found in the intermediate layer, manufactured for a variety of properties and applications.

[0099]

[0099] In various embodiments, for both the core and skin layers, the high refractive index plasticizer is selected such that the refractive index of the plasticizer is at least about 1.460, or greater than about 1.460, or greater than about 1.470, or greater than about 1.480, or greater than about 1.490, or greater than about 1.500, or greater than 1.510, or greater than 1.520. As used herein, “high refractive index plasticizer” is a plasticizer having a refractive index of at least about 1.460. In some embodiments, the high refractive index plasticizer is used in conjunction with a conventional plasticizer, and in some embodiments, if included, the conventional plasticizer is triethylene glycol di-(2-ethylhexanoate) ("3-GEH"), and the refractive index of the plasticizer mixture is at least 1.460. As used herein, the refractive index (also known as the rate of refraction) of the plasticizers or resins used throughout this disclosure is either measured in accordance with ASTM D542 at a wavelength of 589 nm and 25°C, or reported in literature in accordance with ASTM D542.

[0100]

[0100] Examples of plasticizers having a high refractive index that may be used include, but are not limited to, polyadipates (RI of about 1.460 to about 1.485), epoxides (RI of about 1.460 to about 1.480), phthalates and terephthalates (RI of about 1.480 to about 1.540), benzoates (RI of about 1.480 to about 1.550), and other special plasticizers (RI of about 1.490 to about 1.520). Examples of high refractive index plasticizers include, but are not limited to, esters of polybasic acids or polyhydric alcohols, polyadipates, epoxides, phthalates, terephthalates, benzoates, toluates, melitates, and other special plasticizers. Suitable high refractive index plasticizers include, but are not limited to, dipropylene glycol dibenzoate, tripropylene glycol dibenzoate, polypropylene glycol dibenzoate, isodecyl benzoate, 2-ethylhexyl benzoate, diethylene glycol benzoate, propylene glycol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanediol dibenzoate, diethylene glycol di-o-toluate, triethylene glycol di-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate, tri-2-ethylhexyl trimellitate, di-2-ethylhexyl terephthalate, bisphenol A bis(2-ethylhexaonate), ethoxylated nonylphenol, and mixtures thereof.

[0101]

[0101] In various embodiments of the intermediate layer of this disclosure, the intermediate layer contains a total plasticizer of more than 5 phr, about 5 to about 120 phr, about 10 to about 90 phr, about 20 to about 70 phr, about 30 to about 60 phr, or less than 120 phr, or less than 90 phr, or less than 60 phr, or less than 40 phr, or less than 30 phr. Although the total plasticizer content is shown above, the plasticizer content in the skin layer or core layer may differ from the total plasticizer content. In addition, as disclosed in U.S. Patent No. 7,510,771 (the entire disclosure is cited herein by reference), the skin layer and core layer may have different plasticizer types and plasticizer content, to the extent discussed earlier, since the plasticizer content of each layer in equilibrium is determined by the residual hydroxyl group content of each layer. For example, in equilibrium, if the combined thickness of the skin layers is equal to that of the core layer, the intermediate layer may consist of two skin layers, each having 30 phr of plasticizer, and a core layer having 65 phr of plasticizer, for a total plasticizer amount of approximately 45.4 phr for the intermediate layer. With respect to thicker or thinner skin layers, the total plasticizer amount for the intermediate layer will vary accordingly. In various embodiments of the present invention, the plasticizer content of the core layer and skin layers differs by at least 8 phr, or at least 9 phr, or at least 10 phr, or at least 12 phr, or at least 13 phr, or at least 14 phr, or at least 15 phr, or at least 16 phr, or at least 17 phr, or at least 18 phr, or at least 19 phr, or at least 20 phr, or at least 25 phr or more. As used herein, the amount of plasticizer, or any other component in the intermediate layer, can be measured by weight, as parts per 100 parts of resin (phr). For example, if 30 grams of plasticizer are added to 100 grams of polymer resin, the plasticizer content of the resulting plasticized polymer will be 30 phr. As used herein, when the plasticizer content of an intermediate layer is given, the plasticizer content is determined based on the phr of the plasticizer in the mixture or melt used to produce the intermediate layer.

[0102]

[0102] The final intermediate layer, whether formed by extrusion or co-extrusion, is formed via melt fractures of the polymer melt as it exits the extrusion die and therefore generally has a random rough topography, and in addition, the random roughness on one side or both sides (e.g., the skin layer) may be embossed by any embossing method known to those skilled in the art.

[0103]

[0103] While all methods for producing polymer intermediate sheets known to those skilled in the art are considered possible methods for producing the polymer intermediate sheets described herein, this application focuses on polymer intermediate sheets produced by extrusion and co-extrusion processes. The final multilayer glass panel laminate of the present invention is formed using lamination processes known in the art.

[0104]

[0104] Generally, the thickness or standard dimensions of the polymer interlayer sheet are in the range of about 15 mil to 100 mil (about 0.38 mm to about 2.54 mm), about 15 mil to 60 mil (about 0.38 mm to about 1.52 mm), about 20 mil to about 50 mil (about 0.51 to 1.27 mm), and about 15 mil to about 35 mil (about 0.38 to about 0.89 mm). In various embodiments, each of the layers, such as the skin and core layers of the multilayer interlayer, may have a thickness of about 1 mil to 99 mil (about 0.025 to 2.51 mm), about 1 mil to 59 mil (about 0.025 to 1.50 mm), 1 mil to about 29 mil (about 0.025 to 0.74 mm), or about 2 mil to about 28 mil (about 0.05 to 0.71 mm).

[0105]

[0105] In the embodiments described later, the polymer resin is referred to as poly(vinyl butyral)PVB, but it will be understood by those skilled in the art that the polymer may be any polymer suitable for use in multilayer panels. Typical polymers include polyvinyl acetal (PVA) (e.g., PVB or its isomer poly(vinyl isobutyral) (PVisoB), polyurethane (PU), poly(ethylene-co-vinyl acetate) (EVA), polyvinyl chloride (PVC), poly(vinyl chloride-co-methacrylate), polyethylene, polyolefin, ethylene acrylate ester copolymer, poly(ethylene-co-butyl acrylate), silicone elastomer, epoxy resin, and acid copolymers such as ethylene / carboxylic acid copolymers derived from any of the above-mentioned possible thermoplastic resins. Examples include, but are not limited to, remers and their ionomers, as well as combinations thereof. PVB and its isomer PVisoB, polyvinyl chloride, and polyurethane are generally particularly useful polymers for intermediate layers, with PVB (and its isomers) being particularly preferred. For example, a multilayer intermediate layer may consist of PVB / / PVisoB / / PVB. Other examples include PVB / / PVC / / PVB or PVB / / PU / / PVB. Further examples include PVC / / PVB / / PVC or PU / / PVB / / PU.

[0106]

[0106] As used herein, multilayer panels may include a single substrate such as glass, acrylic, or polycarbonate, on which a polymer interlayer sheet is placed, and most commonly, a polymer film is further placed covering the polymer interlayer. The combination of the polymer interlayer sheet and polymer film is commonly referred to as a double layer in the art. A typical multilayer panel having a double layer structure is (glass) / / (polymer interlayer sheet) / / (polymer film), where the polymer interlayer sheet may include multiple interlayers as described above. The polymer film provides a smooth, thin, rigid substrate that offers better optical properties and functions as a performance-enhancing layer than is typically obtained from the polymer interlayer sheet alone. The polymer film differs from the polymer interlayer sheet used herein in that it does not provide the penetration resistance and glass retention properties required by the polymer film itself, but rather provides performance enhancements such as infrared absorption properties. Poly(ethylene terephthalate) ("PET") is the most commonly used polymer film. Generally, as used herein, the polymer film is thinner than the polymer sheet, such as about 0.001 to 0.2 mm thick.

[0107]

[0107] The intermediate layers of the present disclosure comprise two substrates, such as a pair of glass sheets (or other rigid materials known in the art, such as polycarbonate or acrylic), and are most commonly used in multilayer panels in which the intermediate layer is positioned between the two substrates. An example of such a structure is (glass) / / (polymer intermediate sheet) / / (glass), where the polymer intermediate sheet may include multilayer intermediate layers as described above. These examples of multilayer panels are not meant to be limiting, as it will be readily apparent to those skilled in the art that numerous other structures can be fabricated using the intermediate layers of the present disclosure.

[0108]

[0108] A typical glass lamination process includes the following steps: (1) assembling two substrates (e.g., glass) and an intermediate layer; (2) briefly heating the assembly by means of IR radiation or convection; (3) passing the assembly through a pressurized nip roll for a first degassing; (4) a second heating of the assembly to about 60°C to about 120°C to give the assembly sufficient temporary adhesion and seal the edges of the intermediate layer; (5) passing the assembly through a second pressurized nip roll to further seal the edges of the intermediate layer and allow for further handling; and (6) autoclaving the assembly at a temperature between 135°C and 150°C and a pressure between 180 psig and 200 psig for about 30 to 90 minutes. As is known to those skilled in the art, the actual steps, as well as the time and temperature, may vary as needed.

[0109]

[0109] Other means (steps 2-5) known in the art and commercially practiced for use in degassing the intermediate layer-glass interface include vacuum bag and vacuum ring processes in which vacuum is used to remove air.

[0110]

[0110] As previously stated, clarity is a parameter used to describe the polymer interlayers disclosed herein. Clarity is determined by measuring the haze value or percentage haze. Testing for percentage haze is performed using an Illuminant C at a 2-degree observation angle with a haze meter such as the Model D25, available from Hunter Associates (Reston, VA), in accordance with ASTM D1003-61 (Re-approved 1977)-Procedure A. The polymer interlayers are laminated with a pair of clear glass sheets, each 2.3 mm thick (commercially available from Pittsburgh Glass Works, Pennsylvania), and the haze value is measured. The interlayers of this disclosure have a percentage haze of less than about 5%, less than about 4%, less than about 3%, less than about 2%, less than about 1%, or less than about 0.3%.

[0111]

[0111] Transmittance, or Percent Visible Transmittance (%T vis ) is also used to describe the polymer interlayers disclosed herein. Permeability is also measured using an Illuminant D65 at a 10-degree observation angle with a haze meter such as the Model D25, available from Hunter Associates (Reston, VA). The polymer interlayers are laminated with a pair of transparent glass sheets, each 2.3 mm thick (commercially available from Pittsburgh Glass Works, Pennsylvania), and %T vis The following is measured: The polymer intermediates of this disclosure have a %T of more than 85% with respect to intermediates containing only ACA, UV stabilizers, and antioxidants, or more than 80% with respect to intermediates containing additional additives such as pigments, IR absorbers or blockers as mentioned above. vis The polymer intermediate layer containing high levels of pigments and / or dyes is preferably low %T, such as in a polymer intermediate layer where the raw materials are colored or tinted. vis It may have a value.

[0112]

[0112] The refractive index (RI) was measured in accordance with ASTM D542. The reported RI values ​​were obtained at a wavelength of 589 nm at 25°C.

[0113]

[0113] Glass transition temperature (T g ) may be determined by dynamic mechanical thermal analysis (DMTA). DMTA measures the storage (elastic) modulus (G'), loss (viscosity) ratio (G"), and tan delta (=G'' / G') of the sample as a function of temperature and temperature sweep rate at a given frequency. In this specification, a frequency of 1 Hz and a temperature sweep rate of 3 °C / min were used. Then T g It is a temperature scale in °C, determined by the position of the tan delta peak.

[0114]

[0114] The damping loss coefficient (η) may be measured by Mechanical Impedance Measurement as described in ISO 16940. A laminated glass rod sample is prepared, 25 mm wide and 300 mm long, with a pair of 2.3 mm transparent glass plates, and is excited at the center point of the rod by a vibrator (Bruel and Kjaer). An impedance head (Bruel and Kjaer) is used to measure the force and vibration velocity that excite and vibrate the rod, and the resulting conversion function is recorded in the National Instrument data acquisition and analysis system. The loss coefficient in the first vibration mode is calculated using the half-power method.

[0115]

[0115] The "sound transmission loss" (STL) is determined using ASTM E90 (2009) for a laminate of fixed dimensions at a fixed temperature of 20°C. A 2.3 mm clear glass / / "reference interlayer" / / "reference panel" of 2.3 mm clear glass was measured and had a coincidence frequency of 3,150 Hz and an STL of 31 dB at the coincidence frequency, where the "reference interlayer" is produced by mixing 100 parts of poly(vinyl butyral) resin having a residual hydroxyl group content of 18-19 wt.% and 2 wt.% vinyl acetate residue, 38 parts by weight of 3-GEH plasticizer, and other common additives (as described above), and melt extrusion. The reference interlayer has a thickness of 0.76 mm and a glass transition temperature of 30°C. The multilayer interlayer of the present invention or the comparative multilayer interlayer is laminated with 2.3 mm transparent glass by the method described above to produce a reference (or test) laminated glass panel. The panel has dimensions of 50 cm × 80 cm. The STL of the test panel at the coincidence frequency of the "reference panel," for example, the STL at 3,150 Hz, is used to evaluate the sound insulation properties of the panel.

[0116]

[0116] Unless otherwise indicated, all numbers used in this specification and in the claims to represent quantities of mixture components, properties such as molecular weight, reaction conditions, etc., should be understood to be modified in any case by the term "approximately". Accordingly, unless otherwise indicated, the numerical parameters described in the following specification and in the appended claims are approximations that may vary depending on the desired properties to be obtained by the present invention. At a minimum, each numerical parameter should be interpreted by applying the usual rounding method in light of the significant number of digits reported. Furthermore, the ranges presented in this disclosure and in the claims are intended to include the entire range, not just the endpoints. For example, a range presented as 0 to 10 is intended to disclose all integers between 0 and 10, such as 1, 2, 3, 4, etc., all fractions between 0 and 10, such as 1.5, 2.3, 4.57, 6.1113, etc.

[0117]

[0117] Although the numerical ranges and parameters describing the broad scope of the present invention are approximations, the numerical values ​​described in specific examples are intended to be reported accurately, taking into account the measurement methods. However, any numerical value inherently contains a certain degree of error that inevitably arises from the standard deviation found in each of its experimental measurements.

[0118]

[0118] It should be understood that reference to one or more process steps does not exclude the existence of additional process steps before or after the combined enumerated steps, or process steps that fall between those clearly identifiable steps. Furthermore, unless otherwise indicated, names of process steps, mixture components, or other aspects of information disclosed or claimed in this application, such as letters or numbers, are merely convenient means of identifying separate activities or mixture components, and the enumerated letters may be arranged in any order.

[0119] As used herein, unless the context clearly dictates otherwise, the singular forms "a," "an," and "the" include plural referents. For example, C n references to alcohol equivalents are intended to include multiple types of C n alcohol equivalents. Thus, unless the context clearly dictates otherwise, the use of words such as "at least one" or "at least a portion" in one place is not intended to imply that other uses of "a," "an," and "the" exclude plural referents. Similarly, unless the context clearly dictates otherwise, the use of words such as "at least a portion" in one place is not intended to imply that the absence of such words in other places implies "all" is intended.

[0120]

[0120] As used herein, the term "and / or" when used in a listing of two or more items means that any one of the listed items can be employed alone or any combination of two or more of the listed items can be employed. For example, if a composition is described as containing components A, B, and / or C, the composition can contain A alone; B alone; C alone; a combination of A and B; a combination of A and C; a combination of B and C; or a combination of A, B, and C.

[0121]

[0121] Unless specifically indicated otherwise, the present invention may be further illustrated by the following examples of its embodiments, which are included for illustrative purposes only and are not intended to limit the scope of the present invention.

Examples

[0122] Example 1

[0122] A sample of the multilayer sheet was cut into pieces approximately 15 mm in size. 300 g of multilayer chips and 700 g of triethylene glycol bis(2-ethylhexanoate) (3-GEH) were placed in a 1 L glass reactor equipped with a stirrer. The mixture was stirred and heated to 80°C and maintained for 2 hours. The resulting batch was cooled to room temperature and filtered using a Buchner funnel with a 1 mm pore. 5 g of water was added to 500 g of the filtrate and stirred for 1 hour, and the mixture was allowed to settle overnight before centrifugation. After centrifugation, 455 g of clear 3-GEH centrifugated solution and 45 g of precipitate (water and core layer PVB) were obtained.

[0123] Example 2

[0123] A sample of the multilayer sheet was cut into pieces approximately 1.27 centimeters (0.5 inches) in size. 300 g of multilayer chips, 245 g of 3-GEH, and 455 g of centrifugated solution from Example 1 were placed in a 1 L glass reactor. The mixture was stirred and heated to 70°C and maintained for 4 hours. The resulting batch was cooled to room temperature and filtered using a Buchner funnel (with a 1 mm hole). 5 g of water containing 1% KOAC was added to 500 g of the filtrate and stirred for 1 hour. The mixture was allowed to settle overnight before centrifugation. After centrifugation, 480 g of clear 3-GEH centrifugated solution and 20 g of precipitate (water and PVB compound having composition 2) were obtained.

[0124] Example 3

[0124] 300 g of multilayer chips, 245 g of 3-GEH, and 455 g of centrifuged solution from the above example were placed in a 1 L glass reactor. The mixture was stirred and heated to 70°C and maintained for 4 hours. The resulting batch was cooled to 5°C and filtered using a Buchner funnel (with a 1 mm hole). 5 g of water was added to 524 g of the filtrate and stirred for 10 minutes, and the mixture was allowed to settle overnight before centrifugation. After centrifugation, 480 g of clear 3-GEH centrifuged solution and 20 g of precipitate (PVB having water and composition 2) were obtained.

[0125] [Table 1]

[0126] Examples 1-3 describe the treatment applied to granulated multilayer sheet samples obtained after grinding and passing through a 12 mm screen. The total thickness of the multilayer sheet was 0.84 mm, and the core layer thickness was 0.11 mm. The total plasticizer content was 42.1, with 38% plasticizer in the skin layer and 75% plasticizer in the core layer. The skin layer PVB had a hydroxyl group content of 19% and an acetate content of approximately 1.5%. The core layer PVB had a hydroxyl group content of 11% and an acetate content of approximately 1%.

[0127] Example 4

[0125] A sample of the multilayer sheet was cut into small pieces having dimensions of at least one <6 mm. 250 g of multilayer chips and 750 g of triethylene glycol bis(2-ethylhexanoate) (3-GEH) were placed in a 2 L container equipped with a stirrer. The liquid was stirred to 65°C before adding the solid, and then stirred at 55°C for 2 hours after addition. For solid-liquid separation, the slurry batch was transferred to a Buchner funnel with a 1 mm hole. 33 g of 25% potassium acetate aqueous solution was added to 664 g of filtrate and stirred before cooling and centrifugation. After centrifugation, the 3-GEH centrifugation solution was obtained as the liquid phase, and the resulting precipitate was a mixture of water, 3-GEH, and core layer PVB. The varnish precipitate was heated to approximately 130°C at atmospheric pressure in a jacketed stainless steel stirring tank. It was kept in that state for 24 hours until the temperature rose further (indicating that all the water had been removed), and then the mixture was allowed to cool to obtain the varnish.

[0128] Example 5 Varnish recycled for product 1

[0126] Approximately 39.73 kilograms (87.6 pounds) of brand new PVB resin, 2.81 kilograms (6.2 pounds) of multilayer PVB flakes, 9.30 kilograms (20.5 pounds) of triethylene glycol bis(2-ethylhexanoate), and 7.30 kilograms (16.1 pounds) of varnish were blended. The entire mixture was mixed in a batch mixer before being dispensed into an extruder for PVB sheet extrusion.

[0129] Example 6 Varnish recycled for product 2

[0127] 39.73 kilograms (87.6 pounds) of PVB resin, 5.76 kilograms (12.7 pounds) of multilayer PVB flakes, 1.45 kilograms (3.2 pounds) of calcium carbonate, 9.30 kilograms (20.5 pounds) of triethylene glycol bis(2-ethylhexanoate), and 7.30 kilograms (16.1 pounds) of varnish were blended. The entire mixture was mixed in a batch mixer before being discharged into an extruder for PVB sheet extrusion.

[0130] Example 7 Varnish recycled for product 3

[0128] 45.36 kilograms (100 pounds) of PVB core resin, 27.22 kilograms (60 pounds) of triethylene glycol bis(2-ethylhexanoate), and 6.80 kilograms (15.0 pounds) of varnish were blended. The entire mixture was mixed in a batch mixer before being extruded into an extruder for PVB sheet co-extrusion to produce multi-layer PVB products.

[0131] [Table 2] The present invention includes the following embodiments. [1] A method for recovering rigid poly(vinyl butyral) from a plasticized poly(vinyl butyral) multilayer sheet containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral), a. A step of crushing a plasticized poly(vinyl butyral) multilayer sheet to obtain poly(vinyl butyral) granules, b. A step of adding an additional plasticizer to poly(vinyl butyral) granules to remove at least a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules to obtain granules rich in rigid poly(vinyl butyral) and a varnish of soft poly(vinyl butyral) and the additional plasticizer, c. A step of physically separating the rigid poly(vinyl butyral)-rich granular material from the soft poly(vinyl butyral) and additional plasticizer varnish. A method that includes this. [2] The method according to [1], wherein the step of physically separating particulate matter is performed using one or more methods selected from decantation, filtration, or centrifugation. [3] The method according to [1] or [2], wherein the step of removing at least a portion of soft poly(vinyl butyral) from poly(vinyl butyral) granules includes the step of selectively washing off soft poly(vinyl butyral) from poly(vinyl butyral) granules. [4]d. Adding further plasticizers to the granular material which has become rich in rigid poly(vinyl butyral) to remove the additional portion of soft poly(vinyl butyral) from the granular material, e. Separating granular material from additional portions of the flexible poly(vinyl butyral) and further additional plasticizers using one or more methods selected from decantation, filtration, or centrifugation. A method by any of [1] to [3], further including the method by any of [1] to [3]. [5] The method according to any one of [1] to [4], wherein an additional plasticizer is selected from one or more esters of polybasic acids or polyhydric alcohols. [6] The method according to any one of [1] to [5], wherein an additional plasticizer is added to poly(vinyl butyral) granules at a temperature of approximately 25°C to approximately 90°C. [7] The method according to any one of [1] to [6], wherein the additional plasticizer is selected from one or more of the following: triethylene glycol bis(2-ethylhexanoate), tetraethylene glycol bis(2-ethylhexanoate), triethylene glycol bis(2-ethylbutyrate), triethylene glycol diheptanoate, tetraethylene glycol diheptanoate, dihexyl adipate, bis(2-ethylhexyl)adipate, bis(2-ethoxyethyl)adipate, dioctyl adipate, hexylcyclohexyl adipate, diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, adipate polymer, soybean oil, or epoxidized soybean oil. [8] The method according to any one of [1] to [7], wherein the flexible poly(vinyl butyral) has a residual hydroxyl group content of about 8% to about 12%. [9] The method according to any one of [1] to [8], wherein the rigid poly(vinyl butyral) has a residual hydroxyl group content of about 15% to about 25%.

[10] The method according to any one of [1] to [9], wherein the flexible poly(vinyl butyral) has a residual acetate content of less than approximately 15%.

[11] The method according to any one of [1] to

[10] , wherein the rigid poly(vinyl butyral) has a residual acetate content of less than about 5%.

[12] The method according to any one of [1] to

[11] , wherein the flexible poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet contains triethylene glycol bis(2-ethylhexanoate) as a plasticizer.

[13] The method according to any one of [1] to

[12] , wherein the flexible poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet further comprises dihexyl adipate present as a plasticizer.

[14] The method according to any one of [1] to

[13] , wherein triethylene glycol bis(2-ethylhexanoate) is present in a flexible poly(vinyl butyral) in an amount of about 60 phr to about 100 phr.

[15] The method according to any one of [1] to

[14] , wherein the additional plasticizer added to the poly(vinyl butyral) granules in step b) is triethylene glycol bis(2-ethylhexanoate).

[16] The method according to any one of [1] to

[15] , wherein the difference between the residual hydroxyl group content of the flexible poly(vinyl butyral) and the residual hydroxyl group content of the rigid poly(vinyl butyral) is at least 4.0 weight percent.

[17] The method according to any one of [1] to

[16] , wherein the rigid poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet contains approximately 30 phr to approximately 45 phr of plasticizer.

[18] The method according to any one of [1] to

[17] , further comprising the step of isolating the flexible poly(vinyl butyral) and the varnish of an additional plasticizer by subjecting them to one or more of the following: sedimentation, filtration, centrifugation, evaporation, or precipitation.

[19] The method according to any one of [1] to

[18] , further comprising the step of adding a flexible poly(vinyl butyral) and an additional plasticizer varnish to a poly(vinyl butyral) composition.

[20] The method according to

[19] , further comprising the step of forming a poly(vinyl butyral) composition into a sheet.

[21] The method according to any one of [1] to

[20] , further comprising the step of adding a varnish of flexible poly(vinyl butyral) and an additional plasticizer to a poly(vinyl butyral) composition containing a whitening agent to form a translucent intermediate layer.

[22] The method according to any one of [1] to

[21] , further comprising the step of adding a varnish of flexible poly(vinyl butyral) and additional plasticizers to a transparent poly(vinyl butyral) compound. A poly(vinyl butyral) sheet containing the isolated flexible poly(vinyl butyral) described in

[23]

[18] . Laminated glass including the poly(vinyl butyral) sheet described in

[24]

[20] . A poly(vinyl butyral) sheet containing any of the separated, rigid poly(vinyl butyral)-rich granules from

[25] [1] to

[24] . Laminated glass containing any of the poly(vinyl butyral) sheets from

[26] [1] to

[25] .

Claims

1. A method for recovering rigid poly(vinyl butyral) from a plasticized poly(vinyl butyral) multilayer sheet containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral), a. A step of crushing a plasticized poly(vinyl butyral) multilayer sheet to obtain poly(vinyl butyral) granules, b. A step of adding an additional plasticizer to poly(vinyl butyral) granules to remove at least a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules to obtain granules rich in rigid poly(vinyl butyral) and a varnish of soft poly(vinyl butyral) and the additional plasticizer, c. A step of physically separating granular material enriched with rigid poly(vinyl butyral) from a varnish of flexible poly(vinyl butyral) and additional plasticizers. A method that includes this.

2. The method according to claim 1, further comprising the step of adding water and optionally potassium acetate to the varnish to separate additional plasticizers from the water and core layer mixture.

3. The method according to claim 1, wherein the step of physically separating particulate matter is performed using one or more methods selected from decantation, filtration, or centrifugation.

4. The method according to any one of claims 1 to 3, wherein the step of removing at least a portion of soft poly(vinyl butyral) from poly(vinyl butyral) granules includes the step of selectively washing off soft poly(vinyl butyral) from poly(vinyl butyral) granules.

5. d. A step of adding further plasticizer to granular material that has become rich in rigid poly(vinyl butyral) to remove the additional portion of soft poly(vinyl butyral) from the granular material, e. A step of separating granular material from additional portions of the flexible poly(vinyl butyral) and further additional plasticizers using one or more methods selected from decantation, filtration, or centrifugation. The method according to any one of claims 1 to 4, further comprising:

6. The method according to any one of claims 1 to 5, wherein the additional plasticizer is selected from one or more esters of polybasic acids or polyhydric alcohols.

7. The method according to any one of claims 1 to 6, wherein an additional plasticizer is added to poly(vinyl butyral) granules at a temperature of about 25°C to about 90°C.

8. The method according to any one of claims 1 to 7, wherein the additional plasticizer is selected from one or more of the following: triethylene glycol bis(2-ethylhexanoate), tetraethylene glycol bis(2-ethylhexanoate), triethylene glycol bis(2-ethylbutyrate), triethylene glycol diheptanoate, tetraethylene glycol diheptanoate, dihexyl adipate, bis(2-ethylhexyl) adipate, bis(2-ethoxyethyl) adipate, dioctyl adipate, hexylcyclohexyl adipate, diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, adipate polymer, soybean oil, or epoxidized soybean oil.

9. The method according to any one of claims 1 to 8, wherein the flexible poly(vinyl butyral) has a residual hydroxyl group content of about 8% to about 12%.

10. The method according to any one of claims 1 to 9, wherein the rigid poly(vinyl butyral) has a residual hydroxyl group content of about 15% to about 25%.

11. The method according to any one of claims 1 to 10, wherein the flexible poly(vinyl butyral) has a residual acetate content of less than about 15%.

12. The method according to any one of claims 1 to 11, wherein the rigid poly(vinyl butyral) has a residual acetate content of less than about 5%.

13. The method according to any one of claims 1 to 12, wherein the flexible poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet contains triethylene glycol bis(2-ethylhexanoate) present as a plasticizer.

14. The method according to any one of claims 1 to 13, wherein the flexible poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet further comprises dihexyl adipate present as a plasticizer.

15. The method according to any one of claims 1 to 14, wherein triethylene glycol bis(2-ethylhexanoate) is present in a flexible poly(vinyl butyral) in an amount of about 60 phr to about 100 phr.

16. The method according to any one of claims 1 to 15, wherein the additional plasticizer added to the poly(vinyl butyral) granules in step b) comprises triethylene glycol bis(2-ethylhexanoate).

17. The method according to any one of claims 1 to 16, wherein the difference between the residual hydroxyl group content of the flexible poly(vinyl butyral) and the residual hydroxyl group content of the rigid poly(vinyl butyral) is at least 4.0 weight percent.

18. The method according to any one of claims 1 to 17, wherein the rigid poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet contains about 30 phr to about 45 phr of plasticizer.

19. The method according to any one of claims 1 to 18, further comprising the step of isolating the flexible poly(vinyl butyral) and the varnish of an additional plasticizer by subjecting them to one or more of the following: sedimentation, filtration, centrifugation, evaporation, or precipitation.

20. The method according to any one of claims 1 to 19, further comprising the step of adding a flexible poly(vinyl butyral) and an additional plasticizer varnish to a poly(vinyl butyral) composition.

21. The method according to claim 20, further comprising the step of forming a poly(vinyl butyral) composition into a sheet.

22. The method according to any one of claims 1 to 21, further comprising the step of adding a flexible poly(vinyl butyral) and an additional plasticizer varnish to a poly(vinyl butyral) composition containing a whitening agent to form a translucent intermediate layer.

23. The method according to any one of claims 1 to 22, further comprising the step of adding a varnish of flexible poly(vinyl butyral) and an additional plasticizer to a transparent poly(vinyl butyral) compound.

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