Polymer composites with low VOC emissions

Abstract

Disclosed is a thermoplastic composition comprising at least one thermoplastic resin, such as polybutylene terephthalate (PBT), polyethylene terephthalate (PET), thermoplastic polyester elastomer (TPEE), or a combination of two or more of these; an additive which is a weak acid containing a phosphorus element, such as dihydric phosphate; and optionally an inorganic filler, such as reinforcing fibers. The thermoplastic compositions exhibit reduced emission levels of VOCs, such as tetrahydrofuran (THF), in particular upon heating, such as during melt processing, compared to pure thermoplastic resins.

Description

Technical Field

[0001] The present invention relates to thermoplastic compositions having low VOC emissions and good mechanical properties. Background Art

[0002] Several patents, patent applications, and publications are cited in this specification in order to more fully describe the state of the art to which this invention pertains. The entire disclosures of each of these patents, patent applications, and publications are hereby incorporated by reference.

[0003] Polybutylene terephthalate (PBT) is an engineering thermoplastic resin that excels in mechanical, chemical, electronic, and physical properties; therefore, it has been widely used in various applications including automotive parts, consumer electronics, and the like.

[0004] However, when the oligomers in PBT resin are heated in the molten state, for example, during processing steps such as molding or extrusion, they decompose to produce tetrahydrofuran (THF) gas. Outgassing of THF can cause problems such as voids in molded parts, which negatively impacts their mechanical properties. Resins containing PBT are particularly prone to releasing THF within the first week after molding. When the resin or article is subjected to high temperature conditions, THF outgassing accelerates. In consumer applications such as electronic devices or automotive interior components, this outgassing would be unacceptable to consumers.

[0005] Furthermore, many countries have enacted legislation that imposes strict VOC emission limits. To comply with these national laws and regulations, the automotive industry has developed emission requirements that rely on the results of numerous testing procedures. As a result, automotive OEMs have begun to specify low VOC emissions for vehicle interior components.

[0006] For at least these reasons, the development of low THF-emitting PBT is an important consumer amenity and consistent with environmental health and safety principles.

[0007] Others have also attempted to reduce VOC emissions from polymer compositions. For example, U.S. Patent Application No. 2009 / 0039557 describes a method for producing low-emission molded articles from a thermoplastic molding composition comprising PBT, wherein the mold includes one or more vents for venting volatile contents from the heated molding composition.

[0008] US Patent No. 8,148,489 to Peacock et al. describes a method for reducing organic carbon emissions from resins containing PBT blocks by adding a titanium catalyst deactivating compound to the resin after polymerization.

[0009] European Patent No. 683201 describes a modified polybutylene terephthalate resin that reduces the amount of gas such as THF generated during high-temperature use. In this modification, a sulfonic acid compound is added to PBT before completing polycondensation.

[0010] However, there remains a continuing need to reduce VOC emission levels of polymeric materials, particularly when consumers are otherwise exposed to hazardous chemicals such as THF. Summary of the Invention

[0011] Therefore, the present invention provides a polymer composition having low VOC emission levels, such as low THF emission levels. The polymer composition comprises a polymer and a weak acid containing a phosphorus element. Preferably, the polymer comprises PBT, and the weak acid comprises dihydrogen phosphate.

[0012] Also provided is a method for reducing the VOC emission level of a polymer composition, particularly reducing THF emissions of a PBT composition, by adding a weak acid containing elemental phosphorus to the composition, preferably during melt processing, such as during compounding. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Shown is a graph of THF emission levels versus weak acid concentration in polymer compositions of the present invention. DETAILED DESCRIPTION

[0014] A polymer composition having low THF emission levels is described herein. The composition comprises a polymer and a weak acid containing a phosphorus element, such as dihydrogen phosphate. The polymer is preferably a PBT-containing polymer having esterified 1,4-butanediol end groups.

[0015] Without wishing to be bound by theory, it is hypothesized that 1,4-butanediol is a product of hydrolytic deesterification of the PBT-containing polymer to form a polymer having acid end groups. 1,4-butanediol further reacts to form THF.

[0016] Still not wishing to be bound by theory, it is further hypothesized that the weak acid protonates the hydroxyl groups of the butanediol end groups in the first step of the dehydration reaction to form butenol end groups. Even if the butenol end groups are removed by deesterification, they do not react further to form THF. Furthermore, as a non-volatile liquid, butenol does not contribute to the overall VOC emissions of the polymer composition.

[0017] Suitable polymers for the polymer composition include one or more polymers selected from the group consisting of polyethylene terephthalate (PET); polybutylene terephthalate (PBT); copolyetherester elastomers having PBT or PBT segments; copolymeric PBT (i.e., PBT in which some of the 1,4-butanediol is replaced by, for example, one or more other diols, such as aliphatic, cycloaliphatic (e.g., 1,4-cyclohexanedimethanol), or aromatic diols (e.g., 2,2-bis-4-(hydroxyethoxyphenyl)-propane, or in which the terephthalate groups are replaced by residues of other diacids, such as isophthalic acid or adipic acid), and blends of any two or more of these.

[0018] Preferred polymers include one or more polymers selected from PBT, copolymerized PBT, PET, PBT / PET alloys, and copolyetherester elastomers having PET or PBT segments.

[0019] More preferred polymers include one or more polymers selected from PBT, copolymerized PBT, and copolyetherester elastomers having PBT segments.

[0020] Polybutylene terephthalate (PBT) is a more preferred polymer. Suitable PBT polymers are described in U.S. Patent No. 8,148,489 to Peacock et al.

[0021] Suitable PBT polymers can The trademark is commercially available from DuPont Specialty Polymers USA, LLC. Suitable PET polymers can be The trademark is commercially available from DuPont Specialty Polymers USA, LLC.

[0022] Suitable thermoplastic copolyetheresters are described in International Patent Application Publication No. WO2021 / 257534 to Karayianni. In addition, suitable thermoplastic copolyetheresters are available under the trademark (available from DuPont Specialty Polymers USA, LLC of Wilmington, DE) under the trademark Arnitel TM (available from DSM Engineering Materials of Evansville, IN) and Riteflex TM (available from Celanese Corporation, formerly Ticona, Florence, KY).

[0023] The polymer composition may comprise 26.1-99.9% by weight of one or more polymers; preferably 59-99.7% by weight; and more preferably 69.5-99.7% by weight. The weight percentages are based on the total weight of the polymer composition. Furthermore, the weight percentages are complementary, i.e., the sum of the weight percentages of the components of the polymer composition is 100% by weight.

[0024] The polymer composition also contains one or more phosphorus-containing weak acids. Suitable phosphorus-containing weak acids have the following structures:

[0025]

[0026] wherein R is selected from H, OH, optionally substituted C 1-20 Alkyl, optionally substituted C 2-20 Alkylene, optionally substituted C 6-10 Aryl, optionally substituted C 1-20 Alkoxy, polyoxy (C 2-4 ) alkylene and optionally substituted C 6-20 aryloxy, and wherein M is selected from the cation of H, Na, K, Ca, Mg or Al, wherein n is the charge of the cation in the salt, and is the number of anions of the weak acid. However, when R is OH, then M is not H.

[0027] More preferred weak acids contain phosphate elements, including but not limited to dihydrogen phosphate and phenylphosphonate.

[0028] Suitable weak acids containing a phosphate moiety are commercially available from a number of sources, for example, from Sigma-Aldrich Corporation of Burlington, MA.

[0029] The polymer composition may comprise 0.5 to 5 wt% of one or more weak acids containing phosphate elements, preferably 1 to 3 wt% and more preferably 1.5 to 2 wt%. The weight percentages are based on the total weight of the polymer composition and are complementary to the weight percentages of the other components of the polymer composition.

[0030] The polymer compositions disclosed herein may further comprise other additives, such as colorants, antioxidants, UV stabilizers, UV absorbers, heat stabilizers, lubricants, viscosity modifiers, nucleating agents, plasticizers, release agents, scratch and mar modifiers, impact modifiers, emulsifiers, fluorescent whitening agents, antistatic agents, acid adsorbents, odor adsorbents, anti-hydrolysis agents, antimicrobial agents, density modifiers, reinforcing fillers, thermally conductive fillers, flame retardant fillers, glass fibers, electrically conductive fillers, coupling agents, end-capping agents, and combinations of two or more thereof. Such other additives may be present at a level of about 0.005-30 wt %, or about 0.01-25 wt %, or about 0.02-20 wt %, based on the gross weight of the polymer compositions disclosed herein.

[0031] Examples of preferred optional additives include, but are not limited to, lubricants such as RADIA 7176, LOXIOL VPG861, LICOWAX OP, and LICOLUB WE 40; antioxidants such as Irganox 1098 (CAS 23128-74-7), SONGNOX 1010, ANOX 20, and BENOX 1010G; stabilizers such as glycerol propoxylate; and flow improvers such as LOXIOL P861 / 3.5, LIONON DEH-40, VORANOL 2100, and PLASTHALL 809, among others.

[0032] Inorganic fillers are preferred optional additives. When used, the inorganic filler is preferably a flame retardant filler, including but not limited to aluminum hydroxide, magnesium hydroxide, red phosphorus, ammonium polyphosphate, zinc borate, antimony oxide and molybdenum compounds, and combinations of two or more flame retardant fillers.

[0033] Glass fiber is a more preferred inorganic filler. The length of the glass fiber is preferably 4-30 mm, more preferably 4-7 mm. The glass fiber is preferably E-glass fiber (alkali-free glass fiber), C-glass fiber (medium-alkali glass fiber) or A-glass fiber (high-alkali glass fiber). More preferred is E-glass fiber.

[0034] Glass fibers are preferably coated with a coupling agent to enhance their performance as a reinforcing agent. Preferred coupling agents have the general formula: R-Si(OR')3, where R is a functional group capable of interacting with the binder or matrix; R' is typically a methyl or ethyl group. The coupling agent hydrolyzes during use to produce a silanetriol: Si(OH)3. Suitable coupling agents include, but are not limited to, KH-550, KH-560, and KH-570.

[0035] Suitable glass fibers are commercially available from TANSHAN FIBERGLASS CO, LTD of Taian, Shandong, China.

[0036] The polymer composition may contain 5-50 wt% of one or more optional inorganic fillers, such as flame retardant fillers and glass fibers; preferably 15-45 wt%; more preferably 20-40 wt%. The weight percentages are based on the total weight of the polymer composition and are complementary to the weight percentages of the other components of the polymer composition.

[0037] The PBT used in this invention has different viscosities. Under the same conditions, the THF emission levels vary depending on the viscosity. The results show that this method is effective for PBT with varying viscosities. Suitable viscosities range from 0.5 dl / gr to 1.5 dl / gr, with a preferred viscosity of 0.7 dl / gr to 1.2 dl / gr and a more preferred viscosity of 0.8 dl / gr to 1.1 dl / gr.

[0038] The polymer composition can be prepared by any conventional melt blending method, for example in a twin-screw extruder.

[0039] Also provided herein are articles comprising the polymer compositions. Suitable and preferred weak acids and other components of the polymer compositions, suitable and preferred amounts of the weak acids and other components, and suitable and preferred methods for forming the polymer compositions for use in articles are as discussed above with respect to the polymer compositions themselves.

[0040] Examples of articles include, but are not limited to, window lift drive housings, seat adjustment drive housings, various switches and boxes, and steering angle sensors.

[0041] The article can be formed by conventional methods such as injection molding, blow molding or extrusion. A more preferred forming method is injection molding.

[0042] Further provided is a method for reducing THF emissions from a polymer composition. The method includes providing other components of the polymer composition and adding a phosphorus-containing weak acid to the other components. Suitable and preferred phosphorus-containing weak acids and other components of the polymer composition used in this method, suitable and preferred amounts of the phosphorus-containing weak acids and other components, and suitable and preferred methods for forming the polymer composition are as discussed above with respect to the polymer composition itself. Preferably, the phosphorus-containing weak acid is added to the polymer composition during the compounding process.

[0043] VOC emissions from polymer compositions and articles can be further reduced by applying a vacuum to the molten polymer during compounding or molding to capture VOCs such as THF.

[0044] The following examples are provided to further describe the present invention in detail.These examples, which set forth the preferred modes presently contemplated for carrying out the invention, are intended to illustrate and not to limit the invention.

[0045] Embodiments of the Invention

[0046] 1) Molding conditions:

[0047] The examples and comparative examples were molded into 60×60×2 mm and 60×60×1 mm plates under the following conditions:

[0048] Melting temperature: 250℃, 280℃

[0049] Mold temperature: 80℃

[0050] Holding time: 5 minutes

[0051] 2) Gas emission test

[0052] The extent of volatile organic compound emissions from the tested polymer composition is determined by the method described in the Verband der Automobilindustrie [The German Association of the Automotive Industry (VDA)] standard VDA 277. In particular, this refers to the emission of THF, which typically occurs immediately after molding, extruding, or shaping the polymer composition. THF emissions from PBT can be measured using gas chromatography (GC), such as gas chromatography-mass spectrometry (GC-MS).

[0053] After molding the plates, they were stored in sealed aluminum foil bags. For analysis, the plates were removed from the bags and cut into small pieces, which were then tested by GC / MS according to VDA 277. In this method, the GC / MS settings were:

[0054] Oven temperature program GC: constant temperature at 50°C for 3 minutes

[0055] Heating at 200 °C at a rate of 12 K / min

[0056] Keep at 200℃ for 4 minutes

[0057] Injector temperature: 200°C

[0058] Detector temperature: 250°C

[0059] Split ratio: about 1:20

[0060] Carrier gas: Helium

[0061] Intermediate carrier gas velocity: about 22-27 cm / s.

[0062] Calibration: 2,6-di-tert-butyl-4-methylphenol (BHT) must exhibit a retention time of less than 16 minutes when run under the same conditions as the discharge of the polymer composition.

[0063] THF emissions were measured for compositions containing three PBT polymers having different viscosities (ie, different molecular weights).

[0064] 3) Determination of IV (intrinsic viscosity) of PBT according to ASTM D2857

[0065] 4) Materials:

[0066] PBT-1: polybutylene terephthalate with an intrinsic viscosity of 0.7 dl / gr, obtained from CHANG CHUNPLASTICS CO.LTD

[0067] PBT-2: polybutylene terephthalate with an intrinsic viscosity of 0.9 dl / gr, obtained from CHANG CHUNPLASTICS CO.LTD

[0068] PBT-3: polybutylene terephthalate with an intrinsic viscosity of 1.0 dl / gr, obtained from CHANG CHUNPLASTICS CO.LTD

[0069] NaH2PHO4: powder obtained from NAGASE&CO.,LTD.

[0070] Glass fiber: obtained from TANSHAN FIBERGLASS CO, LTD. The grade name is S-1HM436S.

[0071] In each of Comparative Examples CE1-CE6 and Examples E1-E12, polymer compositions were prepared by compounding in an extruder (the weight percentages of the non-PBT components are listed in Table 1). The barrel temperature was set at approximately 250°C, and the screw speed was set at approximately 350 rpm. After exiting the extruder, the blended composition was cooled with water and cut into resin pellets, which were then dried in an electric blower dryer at 90°C for approximately 15 hours.

[0072] The dried resin pellets obtained in Comparative Examples CE1-CE4 and Examples E1-E8 were injection molded into 60×60×2 mm plaques with a melt temperature of 250°C; Comparative Example CE5 and Examples E9-E10 were injection molded into 60×60×1 mm plaques with a melt temperature of 280°C; and Comparative Example CE6 and Examples E11-E12 were injection molded into 60×60×2 mm plaques with a melt temperature of 280°C. The discharge performance of the plaques was measured and is listed in Tables 1, 2, and 3. In these tables, the term "balance" refers to the difference between 100% by weight and the sum of the weight percentages of the other components of the Examples and Comparative Examples.

[0073] In addition, for each sample, the tensile stress at break and the tensile strain were measured according to ISO 527-2:2012; the bending stress was measured according to ISO 178; and the N-charpy impact was measured according to ISO 179-1. The results are listed in Table 1.

[0074] The test results of different NaH2PO4 loading amounts are listed in Table 1 (E1, E5-E8). Figure 1 Optimal ranges for loadings are shown to be greater than 0.3 wt%, greater than 0.5 wt%, or about 3 wt%.

[0075] Table 1

[0076]

[0077] Table 2

[0078]

[0079] Table 3

[0080]

[0081] Although certain preferred embodiments of the present invention have been described and specifically illustrated above, the present invention is not intended to be limited to these embodiments. Various modifications may be made without departing from the scope and spirit of the invention as set forth in the following claims.

Claims

1. A thermoplastic composition comprising: a) at least one thermoplastic resin selected from the group consisting of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and polymers containing a copolymerized PBT component; b) A weak acid containing phosphorus having the following structure: wherein R is selected from the following groups: H, OH, optionally substituted C 1-20 Alkyl, optionally substituted C 2-20 Alkylene, optionally substituted C 6-10 Aryl, optionally substituted C 1-20 Alkoxy, polyoxy (C 2-4 ) alkylene and optionally substituted C 6-20 Aryloxy; wherein M is selected from the cations of H, Na, K, Ca, Mg, Al; where n is the charge of the cation of M; and Provided that when R is OH, M is not H; and c) Other additives.

2. The thermoplastic composition of claim 1, wherein the at least one thermoplastic resin comprises PBT.

3. The thermoplastic composition of claim 1, wherein the at least one thermoplastic resin comprises a thermoplastic copolyetherester having a copolymerized PBT component.

4. The thermoplastic composition of claim 1, wherein the at least one thermoplastic resin is present in an amount of 10 to 99.9 weight percent, based on the total weight of the thermoplastic composition.

5. The thermoplastic composition of claim 1, wherein the weak acid comprises dihydrogen phosphate or phenylphosphonate.

6. The thermoplastic composition of claim 1, wherein the weak acid comprises sodium dihydrogen phosphate, potassium dihydrogen phosphate, or both sodium dihydrogen phosphate and potassium dihydrogen phosphate.

7. The thermoplastic composition of claim 1, wherein the weak acid is present in an amount of 0.01 to about 3 weight percent based on the total weight of the thermoplastic composition.

8. The thermoplastic composition of claim 1, wherein the weak acid is present in an amount of 0.01 to about 2 weight percent, based on the total weight of the thermoplastic composition.

9. The thermoplastic composition of claim 1, wherein the weak acid is present in an amount of 0.01 to about 1 weight percent based on the total weight of the thermoplastic composition.

10. The thermoplastic composition of claim 1, wherein the at least one inorganic filler comprises a flame retardant filler.

11. The thermoplastic composition of claim 1, wherein the flame retardant filler comprises one or more fillers selected from the group consisting of aluminum hydroxide, magnesium hydroxide, red phosphorus, ammonium polyphosphate, zinc borate, antimony oxide, and molybdenum compounds.

12. The thermoplastic composition of claim 1, wherein the optional inorganic filler is a reinforcing filler.

13. The thermoplastic composition of claim 13, wherein the reinforcing filler is selected from the group consisting of glass fiber, silica, talc, mica, carbon black, carbon fiber, aramid fiber, hollow glass spheres, glass flakes, hollow glass beads, milled glass fiber, and combinations of two or more thereof.

14. The thermoplastic composition of claim 1, wherein the optional inorganic filler is present in an amount of 0.01 to about 50 weight percent, based on the total weight of the thermoplastic composition.

15. The thermoplastic composition according to claim 1, further comprising one or more other additives selected from the group consisting of a lubricant, a plasticizer, a colorant, and an antioxidant.

16. A method for reducing VOC emissions from a polymer composition comprising the steps of: a) providing a polymer composition comprising at least one thermoplastic resin selected from the group consisting of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), and a polymer containing a copolymerized PBT component; and optionally an inorganic filler; and b) adding a weak acid containing phosphorus to the polymer composition.

17. The method according to claim 17, further comprising the steps of: c) melting the polymer composition; and d) collecting VOCs emitted from the molten polymer composition by applying a vacuum.

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