Method for recycling poly(vinyl butyral) from multi-layer poly(vinyl butyral) sheets, poly(vinyl butyral) sheets, and laminated glass.

Abstract

A process for recovering flexible poly(vinyl butyral) from poly(vinyl butyral) granules containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral) is disclosed, the process comprising the steps of: adding an additional plasticizer to the poly(vinyl butyral) granules to remove at least a portion of the flexible poly(vinyl butyral) from the poly(vinyl butyral) granules to obtain (i) rigid poly(vinyl butyral)-rich granules and (ii) a varnish of flexible poly(vinyl butyral) and the additional plasticizer; physically separating the granules from the varnish of flexible poly(vinyl butyral) and the additional plasticizer; and adding water to the varnish to obtain a plasticizer layer and a water / flexible poly(vinyl butyral) / plasticizer layer.

Description

[Technical Field]

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

[0002] Laminated safety glass, used in automotive windshields and architectural safety glass, typically consists of two panes of glass laminated together with a plasticizing polymer interlayer between them. Poly(vinyl butyral) ("PVB") is generally the main component of the polymer interlayer.

[0003] Poly(vinyl butyral) resin is typically combined with a plasticizer before melt extrusion into a sheet. Poly(vinyl butyral) resin and plasticizers are usually produced through 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) with butyraldehyde. The properties of poly(vinyl butyral) are determined by its molecular structure, which is characterized by parameters such as molecular weight and its distribution, residual hydroxyl content, and residual acetate content.

[0004] In recent years, the amount of multilayer poly(vinyl butyral) interlayers used in laminated glass has increased and is being applied to laminated safety glass. Multilayer interlayers can enhance sound insulation due to the presence of a softer layer ("core layer") in the center of the sheet. Typically, the composition of the core layer differs from that of the outer layer ("skin layer") in terms of the amount of plasticizer relative to the amount of polymer. The plasticizer content is usually higher in the core layer than in the skin layer. To allow for such differences in composition between layers, the PVB compound in the core layer has a different composition from the PVB compound in the skin layer with respect to the hydroxyl content and, in some cases, also with respect to the residual poly(vinyl acetate) content.

[0005] Conventional multilayer interlayers, such as three-layer acoustic interlayers, contain a soft core layer consisting of a single poly(vinyl butyral) ("PVB") resin with a low residual hydroxyl content and a large amount of conventional plasticizer, and two rigid skin layers with a significantly higher residual hydroxyl content (see, for example, U.S. Patents 5,340,654, 5,190,826, and 7,510,771). Interlayers with the opposite configuration, i.e., an interlayer with one rigid layer sandwiched between two soft layers, have been shown to improve the impact performance of glass panels and can also be designed for sound insulation.

[0006] The following provides a simplified description of how multilayer glass panels are generally manufactured in combination with these interlayers. First, at least one polymer interlayer sheet (single-layer or multilayer) is placed between two substrates, and the excess interlayer is trimmed from the edges to create an assembly. It is not unusual to place multiple polymer interlayer sheets, or polymer interlayer sheets with multiple layers (or a combination of both), within two substrates to create a multilayer glass panel with multiple polymer interlayers. Next, air is removed from the assembly by an applicable process or method known to those skilled in the art, for example, via a nip roller, vacuum bag, or another degassing mechanism. Furthermore, the interlayer is partially crimped to the substrate by any method known to those skilled in the art. In the final step, to form the final single structure, this pre-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 autoclaving (but not limited to autoclaving).

[0007] Trim or off-grade homogeneous poly(vinyl butyral) sheet products can be reused in the sheet manufacturing process. After crushing, the chips or flakes can be added back into the feed of the extrusion process. PVB raw materials can also be recovered from laminated glass after they have served their purpose in actual use. See U.S. Patent Application Publication US2009 / 0209667. However, the presence of a core layer leads to certain visual defects during re-extrusion when such practice is applied to multilayer sheets. Due to differences in the poly(vinyl butyral) composition between the PVB compounds in the skin layer and the core layer, these materials do not mix well in the molten phase. This results in a certain type of haze being observed in laminated glass containing PVB sheets where some of the multilayer sheets were used in the raw material supply, producing products of poor visual quality that are unsuitable for market sale.

[0008] Recycling poly(vinyl butyral) multilayer sheets from off-grade finished sheet products that cannot be reused, and recycling them from laminated glass that serves its primary function and is currently being discarded, can be an economic and ecological step forward. Compared to manufacturing virgin poly(vinyl butyral) resin, recycling finished sheet products can be cost-effective while reducing the environmental footprint of poly(vinyl butyral) resin and sheet manufacturing. Therefore, maximizing scrap reuse is not only a competitive advantage but also an environmentally conscious practice.

[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 then separated from the additives and dissolved foreign polymers present in the solution. Separation of the additives from the solution is carried out in a further step.

[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 including the steps of granulation of laminated glass, solvent extraction of plasticizers and impurities, dissolution of poly(vinyl butyral), prefiltration of insoluble contaminants, color removal by adsorption or bleaching, postfiltration of carbon particles, precipitation of poly(vinyl butyral), and washing, stabilization, and drying of the poly(vinyl butyral) resin. In one embodiment, a method for separating two poly(vinyl butyral) resins from a single batch of granules is disclosed. In this embodiment, the solvent is selected for a dissolution step that selectively dissolves the first poly(vinyl butyral) resin, rather than the second poly(vinyl butyral) resin, at a suitable temperature.

[0011] WO2022150528A1 discloses a process for recovering rigid poly(vinyl butyral) from a plasticized poly(vinyl butyral) multilayer sheet containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral). This process includes crushing the plasticized poly(vinyl butyral) multilayer sheet to obtain granules, adding an additional plasticizer to the granules to remove at least a portion of the flexible poly(vinyl butyral), and physically separating the granules from the resulting solution.

[0012] The need for methods to recycle PVB scrap materials remains. [Overview of the project]

[0013] In one embodiment, the present invention relates to a process for recovering flexible poly(vinyl butyral) from poly(vinyl butyral) granules containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral), the process comprising the steps of adding an additional plasticizer to the poly(vinyl butyral) granules to remove at least a portion of the flexible poly(vinyl butyral) from the poly(vinyl butyral) granules to obtain (i) rigid poly(vinyl butyral)-rich granules and (ii) a varnish of flexible poly(vinyl butyral) and the additional plasticizer. The process comprises the step of physically separating the rigid poly(vinyl butyral)-rich granules from the varnish of flexible poly(vinyl butyral) and the additional plasticizer. A further step according to the present invention comprises adding water to the varnish to obtain a plasticizer layer and a water / flexible PVB / plasticizer layer.

[0014] In one embodiment, the process of the present invention may further include one or more steps of adding further additional plasticizers to the granules to remove the additional portion of flexible poly(vinyl butyral) from the granules, then separating the granules from the additional portion of flexible poly(vinyl butyral) and the further additional plasticizers using one or more techniques selected from water-mediated phase separation, compression, decantation, filtration, or centrifugation, leaving a varnish containing the additional portion of flexible poly(vinyl butyral) and the further additional plasticizers.

[0015] According to a further aspect of the present invention, the resulting varnish is used to produce a poly(vinyl butyral) interlayer or subjected to further separation to isolate the plasticizer and core resin.

[0016] Further aspects of the present invention are disclosed herein and claimed. [Modes for carrying out the invention]

[0017] Accordingly, in a first aspect, the present invention relates to a process for recovering flexible poly(vinyl butyral) from poly(vinyl butyral) granules containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral), the process comprising: a) adding an additional plasticizer to the poly(vinyl butyral) granules to remove at least a portion of the flexible poly(vinyl butyral) from the poly(vinyl butyral) granules to obtain (i) rigid poly(vinyl butyral)-rich granules and (ii) a varnish of flexible poly(vinyl butyral) and the additional plasticizer; b) physically separating the rigid poly(vinyl butyral)-rich granules from the flexible poly(vinyl butyral) and the additional plasticizer; and c) adding water to the varnish to obtain a plasticizer layer and a water / flexible PVB / plasticizer layer.

[0018] In a second embodiment, the plasticizer layer of step c) may be added to the additional plasticizer layer in step a). In various embodiments of the present invention, the process may be carried out continuously and therefore includes a continuous process.

[0019] In a third embodiment, the process may further include the step of adding a solvent to the water / flexible poly(vinyl butyral) / plasticizer layer in step c) to precipitate the flexible PVB from the water / flexible PVB / plasticizer layer, according to any of the embodiments described above.

[0020] In a fourth embodiment, the precipitated poly(vinyl butyral) can be isolated by one or more of the following: centrifugation, small forceps, filtration, or decantation.

[0021] In the fifth embodiment, the step of physically separating the granules according to any of the embodiments described above is performed using one or more techniques selected from decantation, filtration, or centrifugation.

[0022] In a sixth aspect, removing at least a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules, according to any of the foregoing aspects, includes selectively washing away the soft poly(vinyl butyral) from the poly(vinyl butyral) granules.

[0023] In a seventh aspect, according to any of the foregoing aspects, the process may further include adding an additional plasticizer to the physically separated granules rich in rigid poly(vinyl butyral) to remove an additional portion of the soft poly(vinyl butyral) from the granules.

[0024] In an eighth aspect, according to any of the foregoing aspects, the additional plasticizer is selected from one or more of esters of polybasic acids or polyhydric alcohols.

[0025] In a ninth aspect, according to any of the foregoing aspects, the additional plasticizer is added to the poly(vinyl butyral) granules at a temperature of about 25°C to about 90°C.

[0026] In a tenth aspect, according to any of the foregoing aspects, the additional plasticizer is 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.

[0027] In an eleventh aspect, according to any of the foregoing aspects, the soft poly(vinyl butyral) may have a residual hydroxyl content of about 8% to about 12%.

[0028] In the twelfth embodiment, according to any of the embodiments described above, the rigid poly(vinyl butyral) has a residual hydroxyl content of about 15% to about 25%.

[0029] In the 13th embodiment, the flexible poly(vinyl butyral) has a residual acetate content of less than about 15% according to any of the embodiments described above.

[0030] In the 14th embodiment, according to any of the embodiments described above, the rigid poly(vinyl butyral) has a residual acetate content of less than about 5%.

[0031] In the 15th embodiment, the flexible poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet contains triethylene glycol bis(2-ethylhexanoate) present as a plasticizer, according to any of the embodiments described above.

[0032] In the sixteenth embodiment, the flexible poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet further comprises dihexyl adipate present as a plasticizer, according to any of the embodiments described above.

[0033] In the 17th embodiment, triethylene glycol bis(2-ethylhexanoate) is present in a flexible poly(vinyl butyral) in an amount of about 60 phr to about 100 phr, according to any of the embodiments described above.

[0034] In the 18th embodiment, the additional plasticizer added to the poly(vinyl butyral) granules in step b) according to any of the embodiments described above includes triethylene glycol bis(2-ethylhexanoate).

[0035] In the 19th embodiment, according to any of the embodiments described above, the difference between the residual hydroxyl content of the flexible poly(vinyl butyral) and the residual hydroxyl content of the rigid poly(vinyl butyral) is at least 4.0% by weight.

[0036] In the 20th embodiment, according to any of the embodiments described above, the rigid poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet contains approximately 30 phr to approximately 45 phr of plasticizer.

[0037] In a 21st embodiment, the process may further include forming a sheet of a poly(vinyl butyral) composition containing precipitated soft PVB, according to any of the embodiments described above.

[0038] In the 22nd embodiment, the process may further include adding the precipitated soft PVB to a poly(vinyl butyral) composition containing a bleaching agent to form a translucent interlayer, according to any of the embodiments described above.

[0039] In the 23rd embodiment, the process may further include adding the precipitated soft PVB to a clear poly(vinyl butyral) formulation, according to any of the embodiments described above.

[0040] In a 24th aspect, the present invention may include a poly(vinyl butyral) sheet containing precipitated soft PVB, according to any of the preceding aspects.

[0041] In a 25th aspect, the present invention may relate to laminated glass including a poly(vinyl butyral) sheet as described in any of the preceding aspects.

[0042] In a 26th aspect, the present invention may relate to a poly(vinyl butyral) sheet containing precipitated soft PVB as described in any of the prior claims, in accordance with any of the aforementioned aspects.

[0043] In a 27th aspect, the present invention may relate to laminated glass including a poly(vinyl butyral) sheet as described in any of the preceding aspects.

[0044] In the 28th embodiment, the solvent may include water or one or more alcohols having 1 to 8 carbon atoms, according to any of the embodiments described above.

[0045] In the 29th embodiment, the solvent may comprise one or more of water, methanol, ethanol, n-propanol, or i-propanol, according to any of the embodiments described above.

[0046] In the 30th embodiment, the process may further include the step of adding water to rigid poly(vinyl butyral)-rich granules to remove excess plasticizer from the granules, according to any of the embodiments described above.

[0047] Accordingly, in one embodiment, the present invention relates to a process 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 process 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, chips, or the like, without any limitation.

[0048] 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 are rich in rigid poly(vinyl butyral). Thus, these rigid poly(vinyl butyral)-rich granules are in solid form, facilitating the separation of the granules from the resulting soft poly(vinyl butyral) and additional plasticizer. Accordingly, the present invention may also include separating the rigid poly(vinyl butyral)-rich granules from the varnish, along with the soft poly(vinyl butyral) and additional plasticizer described herein, using one or more techniques selected from, for example, decantation, filtration, or centrifugation.

[0049] In further embodiments, the present invention may further include one or more additional steps of adding further additional plasticizers to the granules to remove additional portions of flexible poly(vinyl butyral) from the granules, and then separating the granules from the additional portions of flexible poly(vinyl butyral) and the further additional plasticizer varnish using one or more techniques selected from water-mediated phase separation, compression, 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.

[0050] Therefore, as used herein, the term "varnish" is used to describe the resulting soft poly(vinyl butyral) and additional plasticizers when the granules are rich in rigid poly(vinyl butyral) granules due to the use of plasticizers.

[0051] In important embodiments, the process of the present invention includes: a) 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 (i) rigid poly(vinyl butyral)-rich granules and (ii) a varnish of soft poly(vinyl butyral) and the additional plasticizer; b) physically separating the rigid poly(vinyl butyral)-rich granules from the varnish of soft poly(vinyl butyral) and the additional plasticizer; and c) adding water to the varnish to obtain a plasticizer layer and a water / soft PVB / plasticizer layer (in gel form). This step of adding water to the varnish to obtain a plasticizer layer and a water / soft PVB / plasticizer layer may be considered "water-mediated phase separation," which is a term used to describe the use of water as a phase separation agent. In addition to forming separate layers, we found that water tends to result in more leaching of plasticizer from the resulting granules, which are typically rich in rigid poly(vinyl butyral) that is supersaturated with plasticizer. Thus, we found that this separation technique works remarkably well in removing excess plasticizer from the granules, in addition to what might be considered the usual effects of a mere "phase separation" technique.

[0052] Surprisingly, we discovered that by using plasticizers such as those commonly used to plasticize PVB, it is possible to selectively wash away a portion of the flexible poly(vinyl butyral) from a granulated poly(vinyl butyral) mixture to obtain a varnish that can be used to produce rigid poly(vinyl butyral)-rich granules and poly(vinyl butyral) interlayers. Subsequently, water-mediated phase separation not only separates the free plasticizer by phase separation but also facilitates the leaching of plasticizers that supersaturate the granules.

[0053] In one embodiment, according to any of the embodiments described above, the flexible poly(vinyl butyral) may have a residual hydroxyl content of about 8% to about 12%. In yet another embodiment, the rigid poly(vinyl butyral) may have a residual hydroxyl content of about 15% to about 25%.

[0054] In further embodiments, the plasticized poly(vinyl butyral) multilayer sheet may contain triethylene glycol bis(2-ethylhexanoate) as a plasticizer, according to any of the embodiments described above.

[0055] In yet another embodiment, according to any of the embodiments described above, the plasticized poly(vinyl butyral) multilayer sheet may further contain other useful substances present as plasticizers, such as dihexyl adipate, bis(2-ethylhexyl) adipate, or Benzoflex 9-88 benzoate ester.

[0056] In another embodiment, the additional plasticizer is selected from one or more esters of polybasic acids or polyhydric alcohols, according to any of the embodiments described above. In a further embodiment, the additional plasticizer may be 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, cyclohexyl adipate hexyl, diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, adipate polymer, soybean oil, or epoxidized soybean oil.

[0057] In one embodiment, according to any of the embodiments described above, 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 embodiment, the additional plasticizer added to the poly(vinyl butyral) granules in step b) includes triethylene glycol bis(2-ethylhexanoate).

[0058] In a further embodiment, according to any of the embodiments described above, the difference between the residual hydroxyl content of the flexible poly(vinyl butyral) and the residual hydroxyl content of the rigid poly(vinyl butyral) is at least 4.0% by weight.

[0059] In yet another embodiment, according to any of the embodiments described above, the rigid poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet contains approximately 30 phr to approximately 45 phr of plasticizer.

[0060] In one embodiment, flexible poly(vinyl butyral) can be isolated from a mixture of flexible poly(vinyl butyral) and an additional plasticizer obtained from step b) by sedimentation, filtration, centrifugation, evaporation, or precipitation, according to any of the embodiments described above. In another embodiment, the present invention relates to a poly(vinyl butyral) sheet containing isolated flexible poly(vinyl butyral), and to laminated glass containing this poly(vinyl butyral) sheet.

[0061] In a further embodiment, the varnish of flexible poly(vinyl butyral) and plasticizer obtained according to any of the embodiments described above may optionally be used directly after removing water, without first isolating the flexible poly(vinyl butyral) from the plasticizer, to produce a poly(vinyl butyral) sheet or interfilm containing the varnish.

[0062] In yet another embodiment, according to any of the embodiments described above, the present invention relates to a poly(vinyl butyral) sheet comprising rigid poly(vinyl butyral)-rich separated granules recovered according to the process of the present invention. In yet another embodiment, the present invention relates to laminated glass comprising these poly(vinyl butyral) sheets comprising rigid poly(vinyl butyral)-rich granules.

[0063] In yet another embodiment, the process may further include isolating the flexible poly(vinyl butyral) by subjecting the varnish and additional plasticizers to one or more of the following: sedimentation, filtration, centrifugation, evaporation, or precipitation, according to any of the embodiments described above.

[0064] According to the present invention, step c) of adding water to the varnish may be employed to obtain a plasticizer layer and a water / soft PVB / plasticizer layer. Thus, this "water-mediated phase separation" forms separate layers. Water may also be added to the granules, which tends to result in more leaching of plasticizer from the resulting granules, which are richer in rigid poly(vinyl butyral) than might be expected, probably due to the fact that PVB is usually supersaturated with plasticizer.

[0065] Therefore, surprisingly, it has been discovered that a three-component gel described herein as a “water / flexible poly(vinyl butyral) / plasticizer layer” can be formed using water (or a solution of salt in water), comprising a plasticizer, core (flexible) poly(vinyl butyral), and water. The core or flexible poly(vinyl butyral) can then be isolated by treating the gel with a “solvent,” usually alcohol or an alcohol / water mixture, resulting in the separation of the solid and liquid phases. The former mainly consists of the core poly(vinyl butyral) resin, and the latter mainly consists of water, alcohol, and plasticizer. Each of the above components can then be recovered by various means described herein.

[0066] Therefore, as already described, according to the present invention, a solvent, usually an alcohol / water mixture, can be used. Although we have found that alcohol can be used for such separation, the addition of water helps to prevent the dissolution of soft PVB and thus aids in the separation of PVB.

[0067] In further embodiments, the process may further include adding a flexible poly(vinyl butyral) and an additional plasticizer varnish to the poly(vinyl butyral) composition according to any of the embodiments described above.

[0068] In yet another embodiment, the process may further include forming a poly(vinyl butyral) composition into a sheet according to any of the embodiments described above.

[0069] In another embodiment, according to any of the embodiments described above, the process may further include adding a varnish of flexible poly(vinyl butyral) and additional plasticizers to a poly(vinyl butyral) composition containing a bleaching agent to form a translucent interlayer.

[0070] In yet another embodiment, the process may further include adding a varnish of flexible poly(vinyl butyral) and additional plasticizers to a transparent poly(vinyl butyral) formulation according to any of the embodiments described above.

[0071] In yet another embodiment, according to any of the embodiments described above, the present invention relates to a poly(vinyl butyral) sheet comprising isolated flexible poly(vinyl butyral) according to any of the embodiments described above. In yet another embodiment, the present invention relates to laminated glass comprising a poly(vinyl butyral) sheet according to any of the embodiments described above.

[0072] In yet another embodiment, according to any of the embodiments described above, the present invention may relate to a poly(vinyl butyral) sheet comprising separated granules rich in rigid poly(vinyl butyral) of any of the embodiments described above.

[0073] In yet another embodiment, according to any of the embodiments described above, the present invention may relate to laminated glass including a poly(vinyl butyral) sheet as described in any of the embodiments described above.

[0074] The term “rigid poly(vinyl butyral)” refers, as further described herein, to a poly(vinyl butyral) resin or 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. This rigid poly(vinyl butyral) typically contains a considerable amount of plasticizer, as described elsewhere herein, the amount and type of which may vary depending on the requirements of the sheet from which the granules originate.

[0075] 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. This flexible or core poly(vinyl butyral) also typically contains a considerable amount of plasticizer, as described elsewhere herein, the amount and type of which may vary based on the requirements of the sheet from which the granules originate. In fact, since plasticizers are known to reduce the Tg of PVB, the core of a multilayer sheet may have more plasticizer than the skin or rigid PVB.

[0076] As used herein, the term “plasticizer” generally refers to molecules or blends of molecules that plasticize polymers, such as PVB, and thereby soften them, as further described herein. Since the starting materials of the present invention may be derived from various multilayer sheets whose contents may vary, the plasticizer content may vary. In some embodiments, the plasticizer content may be relatively low, while in other embodiments, additional plasticizers may be added to achieve a much higher plasticizer content. Additional plasticizers may be added up to a saturation point, after which a stable plasticizer content cannot be maintained.

[0077] Furthermore, plasticizers useful in the present invention as additional plasticizers are those with a higher affinity or compatibility to the core layer for the plasticizer, as partially demonstrated by a lower residual hydroxyl content. Therefore, when present as additional plasticizers in higher amounts, they help remove soft poly(vinyl butyral) from granulated poly(vinyl butyral) mixtures by selectively washing or partially dissolving the soft poly(vinyl butyral).

[0078] In some embodiments, the additional plasticizer has hydrocarbon segments with fewer than 20, 15, 12, or 10 carbon atoms. Suitable additional plasticizers for use in the present invention include, among others, 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, cyclohexyl adipate hexyl, diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, adipate polymers, soybean oil, epoxidized soybean oil, and mixtures thereof. A more preferred plasticizer is 3-GEH. Furthermore, to further increase the flow of the interlayer, a plasticizer that is compatible at high temperatures may be preferable.

[0079] As used herein, the term "poly(vinyl butyral) multilayer sheet" refers to a sheet composed of different layers of poly(vinyl butyral) resin, typically having a flexible layer or core layer, with rigid layers or skin layers on each face 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).

[0080] The process of crushing poly(vinyl butyral) multilayer sheets to obtain granular poly(vinyl butyral) mixtures means reducing the size by any suitable means, such as a pulverizer, to obtain granules, chips, flakes, etc., all of which can be considered granules according to the present invention. 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 the particle size. Granulation of the scrap may result in individual granules having a length dimension of less than 2.6 centimeters, or 0.1 to 1.0 centimeters, or 0.4 to 0.8 centimeters. Granules larger than 2.6 centimeters can be used, but generally it is preferable to granulate the sheets into smaller sizes, resulting in a larger total granular surface area. At any point during granulation, the granulated flakes can be sieved to remove contaminants released from the poly(vinyl butyral).

[0081] When additional plasticizers are added to poly(vinyl butyral) granules, this means that the plasticizers added in this step result in a separate liquid phase containing dissolved flexible PVB, in addition to the plasticizers present in the plasticized poly(vinyl butyral) multilayer sheet. It should be noted that some of the additional plasticizers enter the rigid PVB, i.e., when the additional plasticizers come into contact with the plasticized poly(vinyl butyral) layer, they become the same phase as the plasticized poly(vinyl butyral) layer in a supersaturated state. In fact, both flexible poly(vinyl butyral) and rigid poly(vinyl butyral) already contain plasticizers. The additional plasticizers may be the same as the plasticizers present in the flexible poly(vinyl butyral) and / or rigid poly(vinyl butyral), or they may be different from the plasticizers 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 a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules, thereby obtaining the soft poly(vinyl butyral) and plasticizer varnish (forming a separate phase).

[0082] Removing at least a portion of the flexible poly(vinyl butyral) from the poly(vinyl butyral) granules means washing or dissolving a portion of the flexible poly(vinyl butyral) from the granules. The granules can then be separated from the flexible poly(vinyl butyral) and additional plasticizers by one or more techniques such as water-mediated phase separation, decantation, filtration, or centrifugation, as further described herein. Alternatively, the varnish can be used directly to form a poly(vinyl butyral) layer or sheet, or optionally, the additional plasticizers and / or a portion of the residual water can be separated from the varnish before forming a poly(vinyl butyral) sheet or layer from the varnish.

[0083] The fact that the granules are rich in rigid poly(vinyl butyral) means that the relative amount of rigid poly(vinyl butyral) in the granules is higher than before some of the flexible poly(vinyl butyral) was washed away from the granules.

[0084] In one embodiment, a blend of flexible or core poly(vinyl butyral) or flexible poly(vinyl butyral) may have a residual hydroxyl content of about 5% to about 15%, as further described herein. Alternatively, the residual hydroxyl content of core poly(vinyl butyral) may be about 7% to about 13%, or 8% to 12%, or as further described herein.

[0085] In one embodiment, a blend of flexible or core poly(vinyl butyral) or 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.

[0086] The amount of plasticizer in a blend of flexible or core poly(vinyl butyral) or flexible poly(vinyl butyral) may be approximately 50 phr to 150 phr, or 55 phr to 120 phr, or 60 to 100 phr.

[0087] In another embodiment, rigid poly(vinyl butyral) or a blend of rigid poly(vinyl butyral) may have a residual hydroxyl content of about 12% to about 28%, as further described herein. Alternatively, the residual hydroxyl content of rigid poly(vinyl butyral) may be about 15% to about 25%, or 18% to 20%, or as further described herein.

[0088] 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.

[0089] In other embodiments, the residual hydroxyl content of the core layer may be the same as, greater than, or less than the residual hydroxyl content of the resin in the skin layer.

[0090] In one embodiment, the multilayer interlayer may include a first skin polymer layer containing plasticized poly(vinyl butyral) having a molecular weight of less than approximately 140,000 daltons, a second core polymer layer containing plasticized poly(vinyl butyral) having a molecular weight greater than approximately 140,000 daltons, and a third skin polymer layer containing plasticized poly(vinyl butyral) having a molecular weight of less than approximately 140,000 daltons. The second polymer layer is positioned between the first polymer layer and the third polymer layer, resulting in two skin layers and a central core layer.

[0091] In various embodiments of the interlayer of this disclosure, the interlayer may contain a total plasticizer of about 30 to about 60 phr (one-hundredth of a resin). While the total plasticizer content is shown above, the plasticizer content in the skin layer(s) or core layer(s) may differ from the total plasticizer content. Furthermore, the skin layer(s) and core layer(s) may have different plasticizer content, since the plasticizer content of each layer in equilibrium is at least partially determined by its respective residual hydroxyl content. For example, in equilibrium, the interlayer may contain two skin layers, each containing 38 phr of plasticizer, and a core layer containing 75 phr of plasticizer, and if the total thickness of the skin layers is equal to the thickness of the core layer, the total plasticizer content of the interlayer will be about 54.3 phr. For thicker or thinner skin layers, the total plasticizer content of the interlayer may vary accordingly.

[0092] In other embodiments, the amount of plasticizer in a blend of rigid or flexible 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.

[0093] In further embodiments, the difference between the residual hydroxyl content of the flexible poly(vinyl butyral) and the residual hydroxyl 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.

[0094] Accordingly, in various embodiments, the residual hydroxyl content of the poly(vinyl butyral) resin in the skin layer(s) and core layer(s) may vary. The resin for the core layer(s) may contain, for example, about 9 to about 18 weight percent (wt%) of residual hydroxyl groups calculated as PVOH, about 9 to about 16 weight percent (wt%) of residual hydroxyl groups calculated as PVOH, or about 9 to about 14 weight percent (wt%) of residual hydroxyl groups calculated as PVOH. The resin for the skin layer(s) may contain, for example, about 13 to about 35 weight percent (wt%) of residual hydroxyl groups calculated as PVOH, about 13 to about 30 weight percent (wt%) of residual hydroxyl groups calculated as PVOH, or about 15 to about 22 weight percent (wt%) of residual hydroxyl groups calculated as PVOH, and in certain embodiments, it may contain about 17.25 to about 22.25 weight percent (wt%) of residual hydroxyl groups calculated as PVOH, or as otherwise described herein.

[0095] In one embodiment, the flexible poly(vinyl butyral), rigid poly(vinyl butyral), and / or plasticized poly(vinyl butyral) multilayer sheets described herein, or any other poly(vinyl butyral), 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, The materials may contain plasticizers selected from one or more of the following: 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, bis-phenol A bis(2-ethylhexanate), di-(butoxyethyl) terephthalate, di-(butoxyethoxyethyl) terephthalate, bis(2-ethoxyethyl) azipart, or as further described herein.

[0096] In various embodiments, additional plasticizers 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 isobutyrate benzoate, and 1,3-butanediol diben It may comprise one or more of zoate, 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, bis-phenol A bis(2-ethylhexanate), di-(butoxyethyl) terephthalate, and di-(butoxyethoxyethyl) terephthalate, or as further described herein, and may be the same as or different from the plasticizers as described herein, or as further described herein. Additional plasticizers or further plasticizers suitable as plasticizers in flexible poly(vinyl butyral) are described elsewhere herein.

[0097] As described above, the poly(vinyl butyral) multilayer sheet of the present invention typically comprises a rigid poly(vinyl butyral) layer and a flexible poly(vinyl butyral) layer. As stated, the core layer typically comprises flexible poly(vinyl butyral) sandwiched between rigid poly(vinyl butyral) skin layers to form the poly(vinyl butyral) multilayer sheet of the present invention.

[0098] In one embodiment, the amount of additional plasticizer added to the poly(vinylbutyral) granules is sufficient to wash, extract, or selectively dissolve a portion of the flexible poly(vinylbutyral).

[0099] 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.

[0100] In yet another embodiment, an additional plasticizer is added to poly(vinyl butyral) granules in a continuous process, for example, to form a backflow process, which removes 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). The granules can then be separated from the resulting varnish mixture of flexible poly(vinyl butyral) and the additional plasticizer, or the varnish can be used without separating the additional plasticizer from the flexible poly(vinyl butyral), or without partially separating the additional plasticizer from the flexible poly(vinyl butyral), or without separating residual water from the mixture.

[0101] In a further aspect of the present invention, the process may include, after the step of physical separation, a further step of isolating the flexible poly(vinyl butyral) and recovering the plasticizer by subjecting the mixture of the resulting flexible poly(vinyl butyral) and additional plasticizer to one or more of the following: sedimentation, filtration, centrifugation, evaporation, precipitation, or extraction.

[0102] In a further embodiment, the present invention relates to poly(vinyl butyral) sheets containing isolated rigid poly(vinyl butyral), and laminated glass containing these poly(vinyl butyral) sheets.

[0103] In a further embodiment, the present invention relates to poly(vinyl butyral) sheets containing flexible poly(vinyl butyral), regardless of whether the flexible poly(vinyl butyral) is first isolated from the plasticizer, and to laminated glass containing these poly(vinyl butyral) sheets.

[0104] Separating rigid poly(vinyl butyral) from a poly(vinyl butyral) mixture by decantation or sedimentation means, for example, separating the liquid from the rigid poly(vinyl butyral) solid by allowing the solid to settle to the bottom of the container and removing most of the additional plasticizer from the granules.

[0105] Separating rigid poly(vinyl butyral) by filtration means filtering the granular rigid poly(vinyl butyral) solid from the plasticizer.

[0106] Separating rigid poly(vinyl butyral) from a mixture by centrifugal separation means using a centrifuge to separate a solid from a liquid.

[0107] The present invention may be further understood by following the further description below.

[0108] 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 flexible core layers. In one embodiment, these multilayer intermediate 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 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. In the case of 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.

[0109] 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.

[0110] Plasticizers work by embedding themselves between polymer chains, separating them (increasing their "free volume"), and thus significantly lowering the glass transition temperature (Tg) of the polymer resin (typically 0.5-4°C / 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 higher the amount of plasticizer, the lower the Tg. Conventional interlayers generally had Tgs in the range of about 0°C for acoustic (noise reduction) interlayers up to about 45°C, for hurricane and aircraft interlayer applications. The residual OH (or PVOH) in poly(vinyl butyral) determines the equilibrium level of plasticizer that each layer can incorporate. More residual PVOH results in a lower equilibrium level of plasticizer, and therefore a higher Tg layer, and vice versa.

[0111] The glass transition temperature of an interlayer correlates with its stiffness; the higher the glass transition temperature, the stiffer the interlayer. Generally, interlayers with a glass transition temperature of approximately 30°C or higher increase the strength and torsional stiffness of the windshield. On the other hand, soft interlayers (generally characterized by having a glass transition temperature of less than approximately 30°C) contribute to sound dampening (i.e., acoustic properties).

[0112] 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 benzoate The plasticizer may be selected from sobutyrate, 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, bis-phenol A bis(2-ethylhexanate), di-(butoxyethyl) terephthalate, di-(butoxyethoxyethyl) terephthalate, and mixtures thereof, or as otherwise described elsewhere herein. In embodiments, the plasticizer may be a mixture of two or more plasticizers.

[0113] In the embodiment, the haze rate may be less than 0.5% (as measured by ASTM D1003-61 (re-approved 1977)-Procedure A using illuminant C at an observer angle of 2 degrees).

[0114] In the embodiments, the residual hydroxyl 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 usually different from that of the second or core poly(vinyl butyral resin). In the embodiments, the difference between the residual hydroxyl content of the core and the residual hydroxyl content of the skin is at least 4.0 weight percent, or at least 6.0 weight percent.

[0115] 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.

[0116] In the 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.

[0117] In this embodiment, the residual hydroxyl content of the third or skin poly(vinyl butyral resin) is the same as the residual hydroxyl content of the first or core poly(vinyl butyral) resin.

[0118] Multilayer panels are also disclosed. The multilayer panels, as disclosed herein, comprise at least one rigid substrate and a polymer interlayer or a multilayer polymer interlayer. The panels exhibit improved optical properties.

[0119] In one aspect of the present invention, a single plasticizer such as triethylene glycol bis(2-ethylhexanoate), or a mixture thereof with dihexyl adipate, may be used.

[0120] Accordingly, the present invention relates to a method for preferentially removing, washing, or partially dissolving flexible poly(vinyl butyral) resin from poly(vinyl butyral) granules by using a plasticizer as an extractant and utilizing the difference in solubility of PVB components in the plasticizer. This is distinct from the use of conventional, more volatile solvents. Accordingly, the present invention optionally provides a method for reusing raw materials for reintroduction into a manufacturing process without introducing volatile organic compounds and without the need to first isolate the poly(vinyl butyral) resin from the plasticizer.

[0121] Specifically, due to differences in the cloud points of PVB resins of different compositions, as measured by the residual PVOH% in the plasticizer, this technique allows the use of temperature as a key parameter for effectively separating 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 disclosed elsewhere in this specification.

[0122] The present invention also describes a method for removing the PVB resin extracted from the plasticizer extract, thereby enabling the repeated use of the plasticizer in the recovery and recycling operations of core polyvinyl (butyral) resin.

[0123] Accordingly, the present invention describes a method for removing poly(vinyl butyral) extracted from plasticizers in order to enable the repeated use of the solvent during extraction. Poly(vinyl butyral) compounds isolated from multilayer poly(vinyl butyral) sheets having a purity acceptable for reuse may be the result of a process comprising steps described in the present invention as fractionation, extraction, or selective dissolution. In this context, fractionation, extraction, or selective dissolution means that mainly flexible poly(vinyl butyral) is removed or washed from the poly(vinyl butyral) granules, while rigid poly(vinyl butyral) resin remains in the poly(vinyl butyral) granules mainly as a solid in the solvent, and possibly in a swollen state with excess plasticizer.

[0124] Poly(vinyl butyral) compounds are components of multilayer poly(vinyl butyral) sheets, with each layer consisting of poly(vinyl butyral) and plasticizers having different compositions with respect to the poly(vinyl butyral) composition, namely different residual hydroxyl or residual acetate content and plasticizer content. In most cases, the amount of plasticizer differs from the amount of poly(vinyl butyral). Significant extraction of poly(vinyl butyral) compounds from multilayer sheet granules is usually obtained after grinding off-grade sheets into smaller flakes, generally in the range of 1 to 30 mm in size.

[0125] The degree of separation depends on the applied plasticizer, time, and temperature. For example, extraction of core layer PVB from poly(vinyl butyral) multilayer sheets using triethylene glycol bis(2-ethylhexanoate) proceeds to the point where 25–50% of the core layer PVB is removed in a single fractionation step. Repeated extractions increase the degree of separation between different poly(vinyl butyral) compounds. Typically, extraction is achieved when the multilayer sheet or a portion thereof is exposed to a specific solvent within a temperature range of 25–100°C, with extraction times ranging from 5 minutes to several days per extraction cycle.

[0126] Conventional multilayer interlayers, such as three-layer acoustic interlayers, typically contain a soft core layer consisting of a single poly(vinyl butyral) ("PVB") resin having a low residual hydroxyl content and a large amount of conventional plasticizer, and two rigid skin layers having a significantly higher residual hydroxyl content (see, for example, U.S. Patents 5,340,654, 5,190,826, and 7,510,771). Therefore, isolated soft poly(vinyl butyral) can be recycled to form the core layer of a three-layer acoustic interlayer, or the soft poly(vinyl butyral) and plasticizer varnish can be used directly to form a soft poly(vinyl butyral) layer without first separating the two, or the soft poly(vinyl butyral) and plasticizer varnish can be further separated to recover the plasticizer and resin for reuse, for example, using water-mediated separation techniques described herein. The residual hydroxyl content and plasticizer amount in the PVB core resin are optimized so that the intermediate layer provides optimal sound insulation characteristics under ambient conditions for multi-layer glass panels such as windshields and windows installed in vehicles and buildings.

[0127] As used herein, the terms “polymer interlayer sheet,” “interlayer,” and “polymer melt sheet” may generally refer to a single-layer sheet or a multilayer interlayer. A “single-layer sheet,” as its name suggests, is a single polymer layer extruded as one layer. A multilayer interlayer sheet, on the other hand, may include multiple layers, including separately extruded layers, co-extruded layers, or any combination of separately and co-extruded layers. Thus, a multilayer interlayer sheet could include, for example, two or more single-layer sheets combined together (“multilayer sheet”), two or more layers co-extruded together (“co-extruded sheet”), two or more co-extruded sheets combined together, 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 multilayer sheet, and a combination of at least one multilayer sheet and at least one co-extruded sheet. In various embodiments of this disclosure, a multilayer interlayer sheet includes at least two polymer layers (e.g., co-extruded and / or laminated single or multilayer layers) arranged in direct contact with each other, each layer containing a polymer resin, as will be described more fully below. As used herein for multilayer interlayers having at least three layers, “skin layer” generally refers to the outer layer of the interlayer, and “core layer” generally refers to the inner layer(s). Thus, one exemplary embodiment is surface layer / / core layer / / surface layer.

[0128] 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 described, for example, in U.S. Patent Nos. 2,282,057 and 2,282,026, and in Vinyl Acetal Polymers, Encyclopedia of Polymer Science & Technology, 3rd edition, Volume 8, pages 381-399, BEWade (2003), the entirety of which is incorporated herein by reference. The resins are commercially available in various forms, such as Butvar® resin from Solutia Inc., a wholly owned subsidiary of Eastman Chemical Company.

[0129] As used herein, the residual hydroxyl content in PVB (calculated as wt% vinyl alcohol or wt% PVOH) refers to the amount of hydroxyl groups remaining on the polymer chain after processing 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), not all of the acetate groups are usually converted to hydroxyl groups. Furthermore, the reaction with butyraldehyde does not usually convert all hydroxyl groups to acetal groups. Therefore, in any finished PVB resin, residual acetate groups (as vinyl acetate groups) and residual hydroxyl groups will usually be present on the polymer chain. As used herein, the residual hydroxyl content and residual acetate content are measured on a wt% basis according to ASTM D1396.

[0130] The PVB resins of this disclosure typically have molecular weights 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.

[0131] Various adhesion control agents ("ACAs") can be used in the interlayers of this disclosure to control the adhesion of the interlayer sheet to the glass. In various embodiments of the interlayers of this disclosure, the interlayer 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, those disclosed in U.S. Patent No. 5,728,472 (the entire disclosure of which is incorporated herein by reference), sodium residual acetate, potassium acetate, magnesium bis(2-ethyl butyrate), and / or magnesium bis(2-ethylhexanoate).

[0132] Other additives can be incorporated into the intermediate layer to enhance its performance in the final product and to impart specific additional properties to the intermediate layer. 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 cesium tungsten oxide), processing aids, flow-promoting additives, lubricants, impact modifiers, nucleating agents, heat stabilizers, UV absorbers, dispersants, surfactants, chelating agents, coupling agents, adhesives, primers, reinforcing additives, and fillers, among others, which are well known to those skilled in the art.

[0133] In various embodiments of the intermediate layers of this disclosure, the intermediate layer contains a total plasticizer content 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. While the total plasticizer content is indicated above, the plasticizer content in the skin layer(s) or core layer(s) may differ from the total plasticizer content. Furthermore, as disclosed in U.S. Patent No. 7,510,771 (the entire disclosure of which is incorporated herein by reference), the skin layer(s) and core layer(s) may have different types and contents of plasticizers within the above ranges, since the plasticizer content of each layer at equilibrium is determined by the respective residual hydroxyl content of that layer. For example, in equilibrium, the intermediate layer may comprise two skin layers each containing 30 phr of plasticizer and a core layer containing 65 phr of plasticizer, and if the total thickness of the skin layers is equal to the thickness of the core layer, the total amount of plasticizer in the intermediate layer will be approximately 45.4 phr. For thicker or thinner skin layers, the total amount of plasticizer in the intermediate layer will vary accordingly. In various embodiments of the present invention, the plasticizer content of the core layer and skin layers may differ 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, may be measured by weight, as parts per 100 parts of resin (phr). For example, when 30 grams of plasticizer are added to 100 grams of polymer resin, the plasticizer content of the resulting plasticized polymer is 30 phr. In the context of this specification, when the plasticizer content of an intermediate layer is given, the plasticizer content is determined by reference to the phr of the plasticizer in the mixture or melt used to produce the intermediate layer.

[0134] The final intermediate layer, whether formed by extrusion or co-extrusion, generally has a random rough surface topography formed through the melt fracture of the polymer molten material as it exits the extrusion die, and can further be embossed on one or both sides of the random rough surface (e.g., skin layer) by any method of embossing known to those skilled in the art.

[0135] All methods for producing polymer interlayer sheets known to those skilled in the art are intended as possible methods for producing the polymer interlayer sheets described herein, but this application focuses on polymer interlayer sheets produced by extrusion and co-extrusion processes. The final multilayer glass panel laminates of the present invention are formed using lamination processes known in the art.

[0136] Generally, the thickness, or gauge, of the polymer interlayer sheet ranges from approximately 15 mil to 100 mil (approximately 0.38 mm to 2.54 mm), approximately 15 mil to 60 mil (approximately 0.38 mm to 1.52 mm), approximately 20 mil to 50 mil (approximately 0.51 mm to 1.27 mm), and approximately 15 mil to 35 mil (approximately 0.38 mm to 0.89 mm). In various embodiments, each layer of the multilayer interlayer, such as the skin layer and core layer, may have a thickness of approximately 1 mil to 99 mil (approximately 0.025 mm to 2.51 mm), approximately 1 mil to 59 mil (approximately 0.025 mm to 1.50 mm), approximately 1 mil to approximately 29 mil (approximately 0.025 mm to 0.74 mm), or approximately 2 mil to approximately 28 mil (approximately 0.05 mm to 0.71 mm).

[0137] In the embodiments described below, poly(vinyl butyral) PVB is mentioned as the polymer resin, but it will be understood by those skilled in the art that the polymer can be any polymer suitable for use in multilayer panels. Typical polymers include polyvinyl acetal (PVA) (PVB or isomer poly(vinyl isobutyl)) (PVisoB), polyurethane (PU), poly(ethylene-co-vinyl acetate) (EVA), polyvinyl chloride (PVC), poly(vinyl chloride-co-methacrylate), polyethylene, polyolefin, ethylene acrylic acid copolymer, poly(ethylene-co-butyl acrylate), silicone elastomer, epoxy resin, and ethylene / carboxylic acid copolymers derived from any of the aforementioned possible thermoplastic resins. Examples include acid copolymers such as ionomers, and combinations of the aforementioned, but are not limited to these. PVB and its isomer polymer PVisoB, polyvinyl chloride, and polyurethane are generally polymers particularly useful for intermediate layers, with PVB (and its isomer polymers) 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.

[0138] As used herein, a multilayer panel may include a single substrate such as glass, acrylic, or polycarbonate, on which a polymer interlayer sheet is placed, most commonly a polymer film is placed on top of the polymer interlayer. The combination of the polymer interlayer sheet and polymer film is commonly referred to as a two-layer in the art. A typical multilayer panel having a two-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 than those typically obtained with the polymer interlayer sheet alone, and functions as a performance-enhancing layer. Unlike the polymer interlayer sheet used herein, the polymer film does not provide the necessary penetration resistance and glass retention properties on its own, but rather improves properties such as infrared absorption. Poly(ethylene terephthalate) ("PET") is the most commonly used polymer film. Generally, as used herein, the polymer film is thinner than the polymer sheet, for example, about 0.001 to 0.2 mm thick.

[0139] The interlayers of this disclosure are most commonly used in multilayer panels comprising two substrates, such as a pair of glass sheets (or other rigid materials such as polycarbonate or acrylic known in the art), with the interlayer positioned between the two substrates. An example of such a structure is (glass) / / (polymer interlayer sheet) / / (glass), where the polymer interlayer sheet may include the multilayer interlayer as described above. These examples of multilayer panels are not intended to be limiting, and those skilled in the art will readily recognize that numerous other structures can be fabricated using the interlayers of this disclosure.

[0140] A typical glass lamination process includes the following steps: (1) assembling two substrates (e.g., glass) and an interlayer; (2) briefly heating the assembly via IR radiation or convection means; (3) passing the assembly through a pressure nip roll for a first degassing; (4) heating the assembly again to about 60°C to about 120°C to give the assembly temporary adhesion and seal the edges of the interlayer; (5) passing the assembly through a second pressure nip roll to further seal the edges of the interlayer and allow for further handling; and (6) autoclaving the assembly at a temperature of 135°C to 150°C and a pressure of 180 psig to 200 psig for about 30 to 90 minutes. Actual steps, as well as times and temperatures, may vary as needed, as is known to those skilled in the art.

[0141] Other means known in the art and commercially available for use in degassing interlayer glass interfaces (steps 2-5) include vacuum bags and vacuum ring processes that utilize vacuum to remove air.

[0142] As previously stated, clarity is a parameter used to describe the polymer interlayers disclosed herein. Clarity is determined by measuring the haze value or haze rate. The haze rate test is performed using a haze meter such as the Model D25 available from Hunter Associates (Reston, VA) at an observer angle of 2 degrees, using illuminant C, in accordance with ASTM D1003-61 (re-approved in 1977) - Procedure A. The polymer interlayer is laminated with a pair of clear glass sheets 2.3 mm thick (commercially available from Pittsburgh Glass Works of Pennsylvania), and the haze value is measured. The interlayers of this disclosure have haze rates 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%.

[0143] Transparency, or visible transmittance (T vis%) is also used to describe the polymer interlayer disclosed herein. Transparency is also measured in illuminant D65 using a haze meter such as the Model D25 available from Hunter Associates (Reston, VA) at an observer angle of 10 degrees. The polymer interlayer is laminated with a pair of transparent glass sheets 2.3 mm thick (commercially available from Pittsburgh Glass Works of Pennsylvania), and T vis The percentage is measured. The polymer intermediates of this disclosure have a T of more than 85 for intermediates containing only ACA, UV stabilizers, and antioxidants, or more than 80% for intermediates containing additional additives such as pigments, IR absorbers, or blockers as described above. vis It has %. A polymer intermediate containing a high level of pigment and / or dye may, if desired, have a lower T, for example, in a large amount of pigmented or colored polymer intermediate. vis It may have a percentage value.

[0144] Glass transition temperature (T g ) can be determined by dynamic mechanical thermal analysis (DMTA). DMTA measures the storage (elastic) modulus (G'), loss (viscosity) coefficient (G"), and tan delta (=G' / G') of the specimen as a function of temperature at a given frequency and temperature sweep rate. In this specification, a frequency of 1 Hz and a temperature sweep rate of 3 °C / min were used. Then T g This is determined by the position (°C) of the tan delta peak on the temperature scale.

[0145] Damping loss coefficient

number

[0146] The sound transmission loss (STL) is determined at a fixed temperature of 20°C for a laminate of fixed dimensions according to ASTM E90 (2009). The 2.3 mm clear glass / / "Reference Interlayer" / / "Reference Panel" of 2.3 mm clear glass is measured to have an STL of 31 dB at a match frequency of 3,150 Hz, and the "Reference Interlayer" is produced by mixing and melt-extruding 100 parts poly(vinyl butyral) resin having a residual hydroxyl content of 18-19 wt% and a vinyl acetate residue of 2 wt%, 38 wt parts 3-GEH plasticizer, and other common additives (as described above). The Reference Interlayer has a thickness of 0.76 mm and a glass transition temperature of 30°C. The multilayer interlayer or comparative multilayer interlayer of the present invention is laminated with 2.3 mm clear glass according to the above method for producing a reference (or test) laminated glass panel. The panel has dimensions of 50 cm × 80 cm. The STL of the test panel at the matching frequency of the "reference panel," for example, the STL at 3,150 Hz, is used to evaluate the sound insulation properties of the panel.

[0147] Unless otherwise specified, all numbers expressing quantities of ingredients, properties such as molecular weights, reaction conditions, etc., used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, each numerical parameter should be construed in light of the reported number of significant digits and by applying ordinary rounding techniques. Further, the ranges disclosed in the present disclosure and claims are intended to include not only the endpoints, but also the entire range specifically, e.g., a range indicated as 0 to 10 is intended to disclose all integers between 0 and 10 such as 1, 2, 3, 4, etc., all decimals between 0 and 10, e.g., all decimals such as 1.5, 2.3, 4.57, 6.1113, etc., and the endpoints 0 and 10.

[0148] The numerical ranges and parameters setting forth the broad scope of the invention are approximations, but the numerical values recited in specific examples are intended to be reported accurately considering the measurement method. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective test measurements.

[0149] It should be understood that the recitation of one or more process steps does not preclude the presence of additional process steps before or after the combined recited steps or intervening process steps between those expressly identified. Further, unless otherwise indicated, the names of process steps, ingredients, or other aspects of the information disclosed or claimed in this application are convenient means for identifying distinct activities or ingredients, and the recited sequences of characters can be arranged in any order.

[0150] As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise. For example, C nReferences to alcohol equivalents are of multiple types. n It is intended to include the alcohol equivalent. Therefore, even the use of language such as “at least one” or “at least several” in one position is not intended to suggest that other uses of “a,” “an,” and “the” exclude plural references unless the context clearly indicates otherwise. Similarly, the use of language such as “at least several” in one position is not intended to mean that “all” is intended to be absent elsewhere unless the context clearly indicates otherwise.

[0151] As used herein, the term "and / or" means, when used in a list of two or more items, that any one of the listed items may be taken alone, or any combination of two or more of the listed items may be taken. For example, if a composition is described as containing components A, B, and / or C, the composition may include 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.

[0152] The present invention can be further illustrated by the following embodiments, but it should be understood that these embodiments are included solely for illustrative purposes and are not intended to limit the scope of the invention unless otherwise specified. [Examples]

[0153] Example 1. The multilayer sheet sample was cut into approximately 15 mm sections, and 300 g of multilayer chips and 700 g of triethylene glycol bis(2-ethylhexanoate) (3-GEH) were packed into a 1 L glass reactor equipped with a stirrer. The mixture was stirred, heated to 80°C, and held for 2 hours. The resulting batch was cooled to room temperature and filtered through a Buchner funnel with a 1 mm opening. 5 g of water was added to 500 g of the filtrate, stirred for 1 hour, and the mixture was allowed to stand overnight before being centrifuged. After centrifugation, 455 g of a clear 3-GEH concentrate and 45 g of precipitate material (water and core layer PVB) were obtained.

[0154] Example 2. The multilayer sheet sample was cut into sections approximately half an inch in size. 300 g of multilayer chips from Example 1, 245 g of 3-GEH, and 455 g of concentrate were packed into a 1 L glass reactor. The mixture was stirred, heated to 70°C, and held for 4 hours. The resulting batch was cooled to room temperature and filtered through a Buchner funnel (with a 1 mm opening). 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 stand overnight and then centrifuged. After centrifugation, 480 g of clear 3-GEH concentrate and 20 g of precipitate material (PVB compound having water and composition 2) were obtained.

[0155] Example 3. 300 g of multilayer chips, 245 g of 3-GEH, and 455 g of concentrate from the above examples were packed into a 1 L glass reactor. The mixture was stirred, heated to 70°C, and held for 4 hours. The resulting batch was cooled to 5°C and filtered through a Buchner funnel (with a 1 mm opening). 5 g of water was added to 524 g of the filtrate, stirred for 10 minutes, and the mixture was allowed to stand overnight before being centrifuged. After centrifugation, 480 g of clear 3-GEH concentrate and 20 g of precipitate material (PVB having water and composition 2) were obtained. [Table 1]

[0156] Examples 1-3 describe the treatment applied to a granular multilayer sheet sample obtained after grinding and passing through a 12 mm screen. The total thickness of the multilayer sheet was 0.84 mm, and the thickness of the core layer was 0.11 mm. The total plasticizer content was 42.1, with 38 for the skin layer plasticizer and 75 for the core layer plasticizer. The skin layer PVB had a hydroxyl content of 19% and an acetate content of approximately 1.5%. The core layer PVB had a hydroxyl content of 11% and an acetate content of approximately 1%.

[0157] Example 4. In a 1-liter jacketed glass reactor equipped with a two-stage ATF stirrer, 100 parts of extracted, filtered, and centrifuged PVB flakes containing 74.5 phr of plasticizer obtained in the process described in Example 1 were mixed with 900 parts of water at room temperature for 1 hour. The mixture was decanted, and the PVB flakes, with the additional liquid decanted, were centrifuged at 4200 rpm for 10 minutes. After drying overnight in an oven at 50°C, 97.4 parts of PVB flakes were obtained, and the plasticizer filling in the flakes was measured to be 70 phr.

[0158] Example 5. In a 1-liter jacketed glass reactor equipped with a two-stage ATF stirrer, 100 parts of the extracted PVB flakes obtained by the process according to Example 1 were mixed with 900 parts of water at room temperature for 24 hours. The mixture was decanted, and the PVB flakes, with the additional liquid decanted, were centrifuged at 4200 rpm for 10 minutes. After drying overnight in an oven at 50°C, 95.7 parts of PVB flakes were obtained, and the plasticizer filling in the flakes was measured to be 67 phr.

[0159] Example 6. In a 1-liter jacketed glass reactor equipped with a two-stage ATF stirrer, 100 parts of the concentrate isolated as in Example 1 were mixed with 2 parts of 5% KOAc solution for 6 hours. The mixture was centrifuged at 4200 rpm for 10 minutes. 94 parts of a clear upper layer of plasticizer and 6 parts of a cloudy gel layer were obtained. The composition of the gel layer, after drying, was determined to contain 21% water by weight, 65% plasticizer, and 14% LH resin.

[0160] Example 7. 100 parts of the gel layer from Example 6 were dispersed in 200 parts of 190-proof alcohol (ethanol) in a reactor with sufficient stirring to form a uniform slurry around it. The resulting slurry was centrifuged at 4200 rpm for 10 minutes. The supernatant and gel were separated by decantation. The resulting gel was washed and centrifuged twice with 100 parts of 170-proof alcohol. 380 parts of the composite supernatant containing water, ethanol, and plasticizer were recovered for reuse, and the gel was dried to obtain 13 parts of LH resin and 0.7 parts of plasticizer for reuse.

[0161] Example 8. 100 parts of the gel layer from Example 6 were dispersed in 200 parts methanol in a reactor with sufficient stirring to form a uniform slurry around it. The resulting slurry was centrifuged at 4200 rpm for 10 minutes. The supernatant and gel were separated by decantation. The resulting gel was washed and centrifuged twice in 100 parts methanol containing 10% by weight water. 380 parts of the composite supernatant containing water, ethanol, and plasticizer were recovered for reuse, and the gel was dried to obtain 13.5 parts of LH resin and 1 part of plasticizer for reuse.

[0162] Example 9. Multilayer sheet samples were cut into sections having at least one dimension less than 6 mm. 250 g of multilayer chips and 750 g of triethylene glycol bis(2-ethylhexanoate) (3-GEH) were packed into a 2 L setup equipped with a stirrer. Before adding the solid, the liquid was stirred to 65°C, and after addition, it was stirred at 55°C for 2 hours. For solid-liquid separation, the slurry batch was transferred to a Buchner funnel with a 1 mm opening. 33 g of 25% potassium acetate solution in water was added to 664 g of filtrate and stirred before cooling and centrifugation. After centrifugation, a 3-GEH concentrate was obtained as the liquid phase, and the resulting precipitate material was a mixture of water, 3-GEH, and core layer PVB. The varnish precipitate material was heated to 130°C at atmospheric pressure in a jacketed, stirred stainless steel tank. It was held for 24 hours until the temperature rose further (indicating that all water had been removed), and then the mixture was cooled to obtain the varnish.

Claims

1. A process for recovering flexible poly(vinyl butyral) from poly(vinyl butyral) granules containing rigid poly(vinyl butyral) and flexible poly(vinyl butyral), a. Adding an additional plasticizer to the poly(vinyl butyral) granules to remove at least a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules to obtain (i) granules rich in the rigid poly(vinyl butyral), and (ii) a varnish of the soft poly(vinyl butyral) and the additional plasticizer. b. Physically separating the rigid poly(vinyl butyral)-rich granules from the flexible poly(vinyl butyral) and the additional plasticizer varnish, c. The process comprising adding water to the varnish to obtain a plasticizer layer and a water / flexible poly(vinyl butyral) / plasticizer layer.

2. The process according to claim 1, wherein the plasticizer layer of step c) is added to the additional plasticizer layer of step a).

3. The process according to claim 1, further comprising the step of adding a solvent to the water / flexible poly(vinyl butyral) / plasticizer layer of step c) to precipitate the flexible poly(vinyl butyral) from the water / flexible poly(vinyl butyral) / plasticizer layer.

4. The process according to claim 3, further comprising isolating the precipitated soft PVB by one or more of the following: centrifugation, filtration, or decantation.

5. The process according to claim 3 or 4, wherein the solvent comprises one or more of water or alcohols having 1 to 5 carbon atoms.

6. The process according to claim 3 or 4, wherein the solvent comprises one or more of water, methanol, ethanol, n-propanol, i-propanol, t-butanol, i-butanol, or n-butanol.

7. The process according to claim 1, wherein the step of physically separating the granules is performed using one or more techniques selected from decantation, filtration, or centrifugation.

8. The process according to any one of claims 1 to 7, further comprising the step of adding water to the rigid poly(vinyl butyral)-rich granules to remove excess plasticizer from the granules.

9. The process according to any one of claims 1 to 8, wherein removing at least a portion of the soft poly(vinyl butyral) from the poly(vinyl butyral) granules comprises selectively washing away the soft poly(vinyl butyral) from the poly(vinyl butyral) granules.

10. The process according to any one of claims 1 to 9, further comprising the step of adding further additional plasticizers to the physically separated granules rich in rigid poly(vinyl butyral) to remove the additional portion of the soft poly(vinyl butyral) from the granules.

11. The process according to any one of claims 1 to 10, wherein the additional plasticizer is selected from one or more esters of polybasic acids or polyhydric alcohols.

12. The process according to any one of claims 1 to 11, wherein the additional plasticizer is added to the poly(vinyl butyral) granules at a temperature of about 25°C to about 90°C.

13. The process according to any one of claims 1 to 12, 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, cyclohexyl adipate hexyl, diisononyl adipate, heptylnonyl adipate, dibutyl sebacate, adipate polymer, soybean oil, or epoxidized soybean oil.

14. The process according to any one of claims 1 to 13, wherein the flexible poly(vinyl butyral) has a residual hydroxyl content of about 8% to about 12%.

15. The process according to any one of claims 1 to 14, wherein the rigid poly(vinyl butyral) has a residual hydroxyl content of about 15% to about 25%.

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

17. The process according to any one of claims 1 to 16, wherein the rigid poly(vinyl butyral) has a residual acetate content of less than about 5%.

18. The process according to any one of claims 1 to 17, 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.

19. The process according to any one of claims 1 to 18, wherein the flexible poly(vinyl butyral) contained in the plasticized poly(vinyl butyral) multilayer sheet further comprises dihexyl adipate present as a plasticizer.

20. The process according to any one of claims 1 to 19, wherein the triethylene glycol bis(2-ethylhexanoate) is present in the flexible poly(vinyl butyral) in an amount of about 60 phr to about 100 phr.

21. The process according to any one of claims 1 to 20, wherein the additional plasticizer added to the poly(vinyl butyral) granules in step b) comprises triethylene glycol bis(2-ethylhexanoate).

22. The process according to any one of claims 1 to 21, wherein the difference between the residual hydroxyl content of the flexible poly(vinyl butyral) and the residual hydroxyl content of the rigid poly(vinyl butyral) is at least 4.0% by weight.

23. The process according to any one of claims 1 to 22, 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.

24. The process according to any one of claims 1 to 23, further comprising forming a sheet of the poly(vinyl butyral) composition containing the precipitated soft PVB.

25. The process according to any one of claims 1 to 24, further comprising adding the precipitated soft PVB to a poly(vinyl butyral) composition containing a bleaching agent to form a translucent intermediate layer.

26. The method according to any one of claims 1 to 25, further comprising adding the precipitated soft PVB to a transparent poly(vinyl butyral) formulation.

27. A poly(vinyl butyral) sheet containing precipitated soft PVB.

28. Laminated glass comprising the poly(vinyl butyral) sheet described in claim 23.

29. A poly(vinyl butyral) sheet comprising precipitated soft PVB according to any one of claims 1 to 28.

30. Laminated glass comprising a poly(vinyl butyral) sheet according to any one of claims 1 to 29.

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