Resin composition and method for recycling polycarbonate

Abstract

To provide a resin composition including recovered polycarbonate that is resistant to discoloration during melt kneading, and a method for recycling polycarbonate employing the resin composition.SOLUTION: A resin composition comprising a polycarbonate having a phenolic hydroxyl group at one or both ends, and further containing a phosphite antioxidant or a chain extender.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a resin composition and a method for recycling polycarbonate. [Background technology]

[0002] Due to their light weight, transparency, processability, resistance to cracking, and safety in the event of cracking, various transparent plastic materials are used as protective covers for the exteriors of mobile devices, household electrical appliances, industrial electronic devices, automotive electronic devices, etc., particularly for information display units such as monitors. In particular, polycarbonate resin materials are one of the most widely used materials due to their excellent transparency, impact resistance, heat resistance, and processability.

[0003] Patent Document 1 discloses a polycarbonate resin composition that is free from coloration and has excellent hydrolysis resistance, which is obtained by adding a pentaerythritol phosphite compound and a bisphenol organic cyclic phosphite compound or an organic phosphite compound to a polycarbonate resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-41108 Summary of the Invention [Problem to be solved by the invention]

[0005] However, polycarbonate has the drawback of being inferior to glass in surface hardness, abrasion resistance, and scratch resistance, and is easily scratched, and when used as a material for outdoor buildings, it can undergo changes in quality such as deformation, discoloration, and deterioration. As part of carbon neutral efforts, these weather-deteriorated products are collected, crushed, and recycled, but even if the discolored surface layer is removed, the material becomes discolored when melted and kneaded, which creates the problem that it cannot be used as a transparent material.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a resin composition containing recovered polycarbonate that is resistant to discoloration even when melt-kneaded, and a method for recycling polycarbonate using the resin composition. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention employs the following configuration. [1] A resin composition comprising a polycarbonate having a phenolic hydroxyl group at one or both ends, and further comprising a phosphite-based antioxidant or a chain extender. [2] A resin composition comprising a polycarbonate having a phenolic hydroxyl group at one or both ends, and further comprising a chain extender. [3] The resin composition according to [1] or [2], wherein the chain extender is a compound having an oxirane ring skeleton. [4] The resin composition according to any one of [1] to [3], wherein the content of the chain extender relative to the total mass of the resin composition is 0.2 mass% or more.

[0008] [5] The resin composition according to [1], wherein the phosphite-based antioxidant is a compound represented by the following general formula (I) or a compound represented by the following general formula (II): [ka] (In formula (I), R 11 and R 12 are each independently a hydrogen atom, an alkyl group, or an aryl group. [ka] (In formula (II), R 21 is an alkyl group having 1 to 4 carbon atoms; R 22 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R 23 is a fluorine atom or an alkoxy group having 1 to 30 carbon atoms.

[0009] [6] The resin composition according to [1] or [5], wherein the content of the phosphite-based antioxidant relative to the total mass of the resin composition is 0.2 mass% or more. [7] The resin composition according to any one of [1] to [6], wherein when the resin composition is melt-kneaded at 250°C for 20 minutes, the yellowness index (YI) of the resin composition measured in accordance with JIS K 7105 is 10.0 or less. [8] A method for recycling polycarbonate, comprising a step of melt-kneading the resin composition according to any one of [1] to [7]. [Effects of the Invention]

[0010] According to the present invention, there are provided a resin composition containing recovered polycarbonate that is resistant to discoloration even when melt-kneaded, and a method for recycling polycarbonate using the resin composition. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram schematically illustrating the process of condensation of a phenolic hydroxyl group of a polycarbonate having a phenolic hydroxyl group at one or both ends with a compound having an oxirane ring skeleton to produce a repaired condensation resin. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Resin composition> A resin composition according to one embodiment of the present invention contains a polycarbonate having a phenolic hydroxyl group at one or both ends, and further contains a phosphite-based antioxidant or a chain extender.

[0013] [Polycarbonate yellowing mechanism] First, the mechanism of yellowing of polycarbonate will be explained. Polycarbonate recovered from weather-degraded products (sometimes referred to as "recovered polycarbonate" in this specification) contains many polycarbonates having phenolic hydroxyl groups at one or both ends because the main chain is cleaved by light, heat, hydrolysis, or the like. That is, polycarbonates having a phenolic hydroxyl group at one end are significantly increased in recovered polycarbonates, and polycarbonates having phenolic hydroxyl groups at both ends are only detected in recovered polycarbonates.

[0014] [ka]

[0015] Furthermore, when polycarbonate having phenolic hydroxyl groups at one or both ends is melt-kneaded for the purpose of recycling, it is presumed that the terminal portion having the phenolic hydroxyl group is cleaved to produce the following cation:

[0016] [ka] [ka]

[0017] Furthermore, it is presumed that the cation (1) becomes isopropenylphenol (2) during the melt-kneading process, ultimately producing compound (3) that causes yellowing.

[0018] [ka]

[0019] [Polycarbonate] The resin composition according to this embodiment contains a polycarbonate having a phenolic hydroxyl group at one or both ends.

[0020] Examples of the polycarbonate (polycarbonate having a phenolic hydroxyl group at one or both ends) include recycled products of ordinary polycarbonates (recycled polycarbonates).

[0021] The recovered polycarbonate may be, for example, a normal polycarbonate that has been subjected to an external stimulus such as light irradiation, heating, or hydrolysis for a long period of time.

[0022] The ordinary polycarbonate is not particularly limited and various types can be used, but among them, aromatic polycarbonate resins are preferred.

[0023] The weight average molecular weight of the ordinary polycarbonate is preferably 10,000 to 100,000, more preferably 30,000 to 80,000, and even more preferably 40,000 to 60,000.

[0024] The ordinary polycarbonate may be used alone or in combination of two or more kinds, and when two or more kinds are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0025] The above-mentioned ordinary polycarbonates can be produced using a dihydric phenol compound as a raw material by a known method such as the phosgene method, the chloroformate method, or the pyridine method.

[0026] In the resin composition, the ratio of the polycarbonate content (parts by mass) to the total mass (parts by mass) of the resin composition ([the polycarbonate content (parts by mass) of the resin composition)] / [the total mass (parts by mass) of the resin composition]×100) is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be, for example, either 97% by mass or more or 99% by mass or more.

[0027] When the ratio is equal to or more than the lower limit, the transparency, impact resistance, heat resistance, and processability of the resin composition can be further improved. On the other hand, the proportion is preferably 99% by mass or less.

[0028] [Phosphite antioxidant] The resin composition according to this embodiment may contain a phosphite-based antioxidant in addition to the polycarbonate having a phenolic hydroxyl group at one or both ends. The phosphite-based antioxidant decomposes hydroperoxides into stable alcohols, and therefore, when the resin composition contains the phosphite-based antioxidant, the generation of compounds that cause yellowing when the resin composition is melt-kneaded is suppressed.

[0029] Examples of the phosphite antioxidant include compounds represented by the following general formula (I) and compounds represented by the following general formula (II). Among these, the compound represented by general formula (I) is preferred.

[0030] [ka] (In formula (I), R 11 and R 12 are each independently a hydrogen atom, an alkyl group, or an aryl group.

[0031] [ka] (In formula (II), R 21 is an alkyl group having 1 to 4 carbon atoms; R 22 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R 23 is a fluorine atom or an alkoxy group having 1 to 30 carbon atoms.

[0032] (Compound represented by general formula (I)) The compound represented by general formula (I) will be explained below.

[0033] [ka] (In formula (I), R 11 and R 12 are each independently a hydrogen atom, an alkyl group, or an aryl group.

[0034] Examples of the alkyl group include a chain alkyl group (a linear or branched alkyl group), a cycloalkyl group (a cyclic alkyl group), and a chain alkyl group-substituted cycloalkyl group (a group in which one or more hydrogen atoms in a cycloalkyl group are substituted with a chain alkyl group).

[0035] Examples of the aryl group include unsubstituted aryl groups and alkyl group-substituted aryl groups (groups in which one or more hydrogen atoms in an aryl group are substituted with a chain alkyl group or cycloalkyl group).

[0036] Examples of the compound represented by general formula (I) include compounds represented by the following structural formula:

[0037] [ka]

[0038] [ka]

[0039] [ka]

[0040] [ka]

[0041] [ka]

[0042] (Compound represented by general formula (II)) The compound represented by general formula (II) will be explained below.

[0043] [ka] (In formula (II), R 21 is an alkyl group having 1 to 4 carbon atoms; R 22 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R 23 is a fluorine atom or an alkoxy group having 1 to 30 carbon atoms.

[0044] Two R in general formula (II) 21 may be the same as or different from each other.

[0045] Examples of the compound represented by general formula (II) include compounds represented by the following structural formula:

[0046] [ka]

[0047] [ka]

[0048] [ka]

[0049] [ka]

[0050] [ka]

[0051] (Compound represented by general formula (III)) Examples of the phosphite-based antioxidant include the compounds represented by the general formula (I) and the compounds represented by the general formula (II) described above, as well as the compounds represented by the following general formula (III).

[0052] [ka] (In formula (III), R 31 is an alkyl group having 1 to 20 carbon atoms; and n is an integer of 1 to 5.

[0053] Examples of the compound represented by general formula (III) include tris(2,4-di-tert-butylphenyl)phosphite and tris-(2-tert-butyl-4-methylphenyl)phosphite.

[0054] When the resin composition contains a phosphite-based antioxidant, the phosphite-based antioxidant may be used alone or in combination with two or more other types. When two or more other types are used, the combination and ratio thereof can be arbitrarily selected depending on the purpose.

[0055] When the resin composition contains a phosphite-based antioxidant, the content of the phosphite-based antioxidant in the resin composition relative to the total mass of the resin composition is preferably 0.2 mass% or more, more preferably 0.3 mass% or more and 2 mass% or less, and even more preferably 0.4 mass% or more and 1.5 mass% or less. When the ratio is equal to or greater than the lower limit, the generation of compounds that cause yellowing when the resin composition is melt-kneaded is further suppressed, and when the ratio is equal to or less than the upper limit, the excessive use of the phosphite-based antioxidant is further suppressed.

[0056] When the resin composition contains a plurality of phosphite-based antioxidants (for example, a compound represented by general formula (I), a compound represented by general formula (II), etc.), it is preferable that the ratio of the total content of the plurality of phosphite-based antioxidants to the total mass of the resin composition is in the same numerical range as the content ratio of the above-mentioned phosphite-based antioxidants.

[0057] [Chain extender] The resin composition according to this embodiment may contain a chain extender in addition to the polycarbonate having a phenolic hydroxyl group at one or both ends.

[0058] In this specification, the term "chain extender" refers to an additive that bonds with a phenolic hydroxyl group of a polycarbonate having a phenolic hydroxyl group at one or both ends, thereby linking the polycarbonate together.

[0059] The resin composition contains a chain extender, and the phenolic hydroxyl groups of the polycarbonate having phenolic hydroxyl groups at one or both ends thereof bond with the chain extender to link the polycarbonate units together, thereby suppressing the generation of isopropenylphenol and, in turn, the generation of compounds that cause yellowing, even when the resin composition is melt-kneaded.

[0060] Examples of the chain extender include a compound having an oxirane ring skeleton, an isocyanate compound, and a diamine compound.

[0061] 1 , compound 2 having an oxirane ring skeleton opens the oxirane ring and condenses with the phenolic hydroxyl group of polycarbonate 1 having phenolic hydroxyl groups at one or both ends, linking the polycarbonates 1 together to produce a repaired condensation resin 3. Therefore, when the resin composition contains compound 2 having an oxirane ring skeleton, the production of isopropenylphenol, and therefore the production of compounds that cause yellowing, is further suppressed even when the resin composition is melt-kneaded.

[0062] In this specification, the term "oxirane skeleton" refers to a skeleton having a structure in which one or more hydrogen atoms have been removed from an oxirane.

[0063] When the resin composition contains a chain extender, the chain extender may be one type only, or two or more types. When two or more types are used, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0064] When the resin composition contains a chain extender, the content of the chain extender in the resin composition relative to the total mass of the resin composition is preferably 0.2 mass% or more, more preferably 0.5 mass% or more and 10 mass% or less, and even more preferably 0.8 mass% or more and 7 mass% or less. When the ratio is equal to or greater than the lower limit, the generation of compounds that cause yellowing when the resin composition is melt-kneaded is further suppressed.When the ratio is equal to or less than the upper limit, the excessive use of the chain extender is further suppressed.

[0065] The resin composition may contain one or more phosphite antioxidants and one or more chain extenders.

[0066] [Other ingredients] The resin composition may contain only a polycarbonate having a phenolic hydroxyl group at one or both ends and a phosphite antioxidant or a chain extender (i.e., it may consist of a polycarbonate having a phenolic hydroxyl group at one or both ends and a phosphite antioxidant or a chain extender), or it may further contain a component (sometimes referred to herein as "other component") that does not fall into any of the categories of a polycarbonate having a phenolic hydroxyl group at one or both ends, a phosphite antioxidant, and a chain extender (i.e., it may consist of a polycarbonate having a phenolic hydroxyl group at one or both ends, a phosphite antioxidant, or a chain extender, and the other component).

[0067] The other components contained in the resin composition are not particularly limited and can be selected arbitrarily depending on the purpose. For example, the other components may be either resin components or non-resin components. The other component, which is a resin component, is a polycarbonate that does not have a phenolic hydroxyl group at one or both ends (sometimes referred to as a "new polycarbonate" in this specification) or a resin other than polycarbonate. The other component, which is a resin component, may be a homopolymer, which is a polymer of one type of monomer, or a copolymer, which is a polymer of two or more types of monomers.

[0068] Examples of the other non-resin components include additives known in the art. Examples of the additives include antifogging agents, antioxidants other than phosphite-based antioxidants, antistatic agents, crystal nucleating agents, inorganic particles, viscosity reducers, thickeners, heat stabilizers, infrared absorbers, and ultraviolet absorbers.

[0069] The resin composition may contain only one type of other component, or two or more types. When two or more types are contained, the combination and ratio thereof can be selected arbitrarily depending on the purpose.

[0070] <Characteristics of resin composition> [Yellowness (YI)] The yellowness index (YI) of the resin composition after melt-kneading can be measured, for example, in accordance with JIS K7105. When the resin composition is melt-kneaded at 250°C for 20 minutes, the yellowness index (YI) of the resin composition is preferably 10.0 or less, more preferably 6.0 or less, and even more preferably 3.0 or less.

[0071] The yellowness index (YI) of the resin composition after melt-kneading can be adjusted by adjusting the type or content of the components contained in the resin composition. For example, the yellowness index (YI) of the resin composition after melt-kneading can be easily adjusted by adjusting the type or content of the phosphite antioxidant or chain extender contained in the resin composition.

[0072] <How to recycle polycarbonate> A method for recycling polycarbonate according to one embodiment of the present invention includes a step of melt-kneading the resin composition.

[0073] The temperature during melt-kneading is not particularly limited, but is preferably 250° C. to 320° C. When the temperature is equal to or higher than the lower limit, the fluidity is improved. When the temperature is equal to or lower than the upper limit, burning is reduced. [Example]

[0074] The present invention will be described in more detail below with reference to specific examples, although the present invention is not limited to the examples shown below.

[0075] [Example 1] <Production of Resin Composition> A resin composition was produced according to the following procedure.

[0076] Polycarbonate that had been exposed outdoors for more than 10 years was collected and crushed to prepare recycled polycarbonate.

[0077] The recovered polycarbonate (95.0% by mass) and a chain extender (BASF's "Joncryl (registered trademark) ADR4468") (5.0% by mass) were mixed to obtain a resin composition, which was then melt-kneaded at 250°C for 20 minutes.

[0078] <Evaluation of Resin Composition> The yellowness index (YI) of the resin composition obtained above was measured in accordance with JIS K7105. The results are shown in Table 1.

[0079] [Example 2] A resin composition was produced and evaluated in the same manner as in Example 1, except that the content of the recovered polycarbonate was changed from 95.0% by mass to 99.0% by mass and the content of the chain extender was changed from 5.0% by mass to 1.0% by mass. The results are shown in Table 1.

[0080] [Example 3] The recovered polycarbonate (99.0% by mass) was mixed with 1.0% by mass of a phosphite-based antioxidant A (ADEKA CORPORATION's "ADEKA STAB PEP-36") to obtain a resin composition. The resin composition was then melt-kneaded at 250°C for 20 minutes.

[0081] The phosphite-based antioxidant A is 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5,5]undecane, which is represented by the following structural formula. [ka]

[0082] The resin composition obtained above was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0083] [Example 4] A resin composition was produced and evaluated in the same manner as in Example 3, except that the content of the recovered polycarbonate was changed from 99.0% by mass to 99.9% by mass and the content of the phosphite-based antioxidant A was changed from 1.0% by mass to 0.1% by mass. The results are shown in Table 1.

[0084] [Example 5] The recovered polycarbonate (99.0% by mass) was mixed with phosphite antioxidant B (ADEKA CORPORATION's "ADEKA STAB HP-10") (1.0% by mass) to obtain a resin composition. The resin composition was then melt-kneaded at 250°C for 20 minutes.

[0085] The phosphite-based antioxidant B is 2,2'-methylenebis(4,6-di-tert-butylphenyl)2-ethylhexyl phosphite, which is represented by the following structural formula. [ka]

[0086] The resin composition obtained above was evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0087] [Comparative Example 1] The recovered polycarbonate (99.0% by mass) and a phenolic antioxidant (ADEKA CORPORATION's "ADEKA STAB AO-80") (1.0% by mass) were mixed to obtain a resin composition, which was then melt-kneaded at 250°C for 20 minutes.

[0088] The phenolic antioxidant is 3,9-bis{2-[3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5.5]undecane, which is represented by the following structural formula.

[0089] [ka]

[0090] The resin composition obtained above was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0091] Comparative Example 2 A resin composition was produced and evaluated in the same manner as in Comparative Example 1, except that the content of the recovered polycarbonate was changed from 99.0% by mass to 99.9% by mass and the content of the phenolic antioxidant was changed from 1.0% by mass to 0.1% by mass. The results are shown in Table 2.

[0092] Comparative Example 3 A resin composition was produced and evaluated in the same manner as in Example 1, except that the content of the recovered polycarbonate was changed from 95.0% by mass to 100% by mass and the chain extender was not added. The results are shown in Table 2.

[0093] Comparative Example 4 A resin composition was produced and evaluated in the same manner as in Comparative Example 1, except that virgin polycarbonate ("E2000" manufactured by Mitsubishi Chemical Corporation) was pulverized without being exposed to the outdoors instead of the recycled polycarbonate. The results are shown in Table 2.

[0094] [Table 1]

[0095] [Table 2]

[0096] As is clear from the above results, the resin compositions of Examples 1 to 5 contained recycled polycarbonate and further contained a phosphite-based antioxidant or a chain extender, and therefore had a yellowness index (YI) of 2.1 to 22.1, which was lower than the yellowness index (23.1) of Comparative Example 3, which contained only recycled polycarbonate, and it was confirmed that the resin compositions were less likely to discolor even when melt-kneaded.

[0097] The resin compositions of Examples 1 and 2 contained recycled polycarbonate and further contained a chain extender, and therefore had a yellowness index (YI) of 2.1 to 5.8, which was lower than the yellowness index (10.0 to 22.1) of Examples 3 to 5, which contained recycled polycarbonate and further contained a phosphite-based antioxidant, and it was confirmed that they were less likely to discolor even when melt-kneaded.

[0098] The resin composition of Example 3 contained recycled polycarbonate and further contained 1.0 mass% of phosphite-based antioxidant A, and therefore had a yellowness index (YI) of 10.0, which was lower than the yellowness index (15.8) of Comparative Example 1, which contained recycled polycarbonate and further contained 1.0 mass% of a phenol-based antioxidant, and it was confirmed that the resin composition was resistant to discoloration even when melt-kneaded.

[0099] The resin composition of Example 4 contained recycled polycarbonate and 0.1% by mass of phosphite-based antioxidant A, and therefore had a yellowness index (YI) of 15.8, which was lower than the yellowness index (23.1) of Comparative Example 2, which contained recycled polycarbonate and 0.1% by mass of a phenol-based antioxidant, and it was confirmed that the resin composition was less susceptible to discoloration even when melt-kneaded. [Industrial Applicability]

[0100] The polycarbonate recycling method of the present invention is applicable to the recycling of materials for outdoor buildings such as carports, verandas, terraces, and arcades. [Explanation of symbols]

[0101] 1. Polycarbonate with terminal phenolic hydroxyl groups 2. Chain extender 3. Interlocked polycarbonate

Claims

1. A resin composition comprising a polycarbonate having a phenolic hydroxyl group at one or both ends, and further comprising a phosphite-based antioxidant or a chain extender.

2. A resin composition comprising a polycarbonate having a phenolic hydroxyl group at one or both ends, and further comprising a chain extender.

3. The resin composition according to claim 1 or 2, wherein the chain extender is a compound having an oxirane ring skeleton.

4. The resin composition according to claim 1 or 2, wherein the content of the chain extender in the resin composition is 0.2 mass % or more relative to the total mass of the resin composition.

5. The resin composition according to claim 1, wherein the phosphite-based antioxidant is a compound represented by the following general formula (I) or a compound represented by the following general formula (II): 【Chemical 1】 (In formula (I), R １１ and R １２ are each independently a hydrogen atom, an alkyl group, or an aryl group. 【Chemistry 2】 (In formula (II), R ２１ is an alkyl group having 1 to 4 carbon atoms; R ２２ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms; R ２３ is a fluorine atom or an alkoxy group having 1 to 30 carbon atoms.

6. The resin composition according to claim 1, wherein the content of the phosphite-based antioxidant in the resin composition is 0.2 mass% or more relative to the total mass of the resin composition.

7. 3. The resin composition according to claim 1, wherein the resin composition has a yellowness index (YI) of 10.0 or less, as measured in accordance with JIS K 7105, when melt-kneaded at 250°C for 20 minutes.

8. A method for recycling polycarbonate, comprising a step of melt-kneading the resin composition according to claim 1 or 2.

Images