Thermoplastic resin composition and article produced therefrom

Abstract

A thermoplastic resin composition of the present invention comprises: approximately 100 parts by weight of a polybutylene terephthalate resin; approximately 10-40 parts by weight of a polycarbonate resin; and approximately 20-100 parts by weight of glass fibers having an A value of approximately 30-110 in equation 1. The thermoplastic resin composition has excellent metal adhesion, stiffness, flowability, a balance of such physical properties, and the like.

Description

Thermoplastic resin composition and molded article manufactured therefrom

[0001] The present invention relates to a thermoplastic resin composition and a molded article manufactured therefrom. More specifically, the present invention relates to a thermoplastic resin composition having excellent metal bonding properties, rigidity, fluidity, and a balance of these properties, and a molded article manufactured therefrom.

[0002]

[0003] Nanomolding technology (NMT) is a process that involves injection molding thermoplastic resins with metal inserts for specific purposes. In these applications, the bonding strength between the metal and thermoplastic resin is crucial.

[0004] As engineering plastics, polyester resins, blends of polyester resins, and polycarbonate resins each exhibit useful properties and are used in various applications, including nanomolding technology.

[0005] However, polyester resin has a problem in that it has a fast crystallization rate, which reduces fluidity (moldability) under various molding conditions.

[0006] To address this, attempts have been made to improve mechanical properties, such as rigidity, by mixing additives such as inorganic fillers into polyester resins. For example, polybutylene terephthalate (PBT) materials reinforced with inorganic fillers such as glass fibers are used in applications such as mobile and automotive components. However, these materials also have problems, such as reduced metal bonding and fluidity (moldability) during molding.

[0007] Therefore, there is a need to develop a thermoplastic resin composition with excellent metal bonding properties, rigidity, fluidity, and a balance of these properties.

[0008] The background technology of the present invention is disclosed in Korean Patent No. 10-0709878, etc.

[0009]

[0010] The purpose of the present invention is to provide a thermoplastic resin composition having excellent metal bonding properties, rigidity, fluidity, and a balance of these properties.

[0011] Another object of the present invention is to provide a molded article formed from the thermoplastic resin composition.

[0012] The above and other objects of the present invention can all be achieved by the present invention described below.

[0013]

[0014] 1. One aspect of the present invention relates to a thermoplastic resin composition. The thermoplastic resin composition comprises: about 100 parts by weight of polybutylene terephthalate resin; about 10 to about 40 parts by weight of polycarbonate resin; and about 20 to about 100 parts by weight of glass fiber having an A value of about 30 to about 110 of the following formula 1:

[0015] [Formula 1]

[0016] A = (M × C) / 100

[0017] In the above formula 1, M is the magnesium (Mg) content value of the glass fiber (unit: ppm), and C is the content value of the surface treatment material among 100 wt% of the total glass fiber (unit: wt%).

[0018] 2. In the above 1 specific example, the polybutylene terephthalate resin may have an intrinsic viscosity [η] measured according to ASTM D2857 of about 0.5 to about 1.5 dl / g.

[0019] 3. In the above 1 or 2 specific examples, the polycarbonate resin may have a weight average molecular weight of about 10,000 to about 50,000 g / mol as measured by GPC (gel permeation chromatography).

[0020] 4. In the above 1 to 3 specific examples, the weight ratio of the polycarbonate resin and the glass fiber may be about 1:1 to about 1:7.

[0021] 5. In the above 1 to 4 specific examples, the thermoplastic resin composition may have a metal bonding strength of about 30 to about 50 MPa, measured after bonding an aluminum-based metal specimen of 1.2 cm × 4 cm × 0.3 cm in size and a thermoplastic resin composition specimen of 1.2 cm × 4 cm × 0.3 cm in size through insert injection molding so that the 1.2 cm × 0.3 cm cross-sections of each specimen are attached to each other, according to ISO 19095.

[0022] 6. In the above 1 to 5 specific examples, the thermoplastic resin composition has a tensile strength of about 1,350 to about 1,850 kgf / cm of a 3.2 mm thick specimen measured under conditions of 5 mm / min according to ASTM D638. 2 It could be.

[0023] 7. In the above 1 to 6 specific examples, the thermoplastic resin composition may have a spiral flow length of about 110 to about 130 mm when measured after injection molding in a spiral-shaped mold having a width of 10 mm and a thickness of 1 mm under conditions of a molding temperature of 280°C, a mold temperature of 150°C, an injection pressure of 100 MPa, and an injection speed of 100 mm / s.

[0024] 8. Another aspect of the present invention relates to a molded article. The molded article is characterized in that it is formed from a thermoplastic resin composition according to any one of 1 to 7 above.

[0025] 9. Another aspect of the present invention relates to a composite material. The composite material is characterized by comprising: a plastic member formed from a thermoplastic resin composition according to any one of 1 to 7; and a metal member in contact with the plastic member.

[0026] 10. In the above 9 specific examples, the metal member may include one or more metals selected from aluminum, titanium, iron, and zinc.

[0027]

[0028] The present invention has the effect of providing a thermoplastic resin composition having excellent metal bonding properties, rigidity, fluidity, and a balance of these properties, and a molded product (such as a plastic member of a composite material) formed therefrom.

[0029]

[0030] Hereinafter, the present invention will be described in detail as follows.

[0031] A thermoplastic resin composition according to the present invention comprises (A) polybutylene terephthalate resin; (B) polycarbonate resin; and (C) glass fiber.

[0032] In this specification, “a to b” indicating a numerical range is defined as “≥a and ≤b”.

[0033]

[0034] (A) Polybutylene terephthalate resin

[0035] According to one specific example of the present invention, a polybutylene terephthalate (PBT) resin can be applied together with a polycarbonate resin, a specific glass fiber, etc. to improve the metal bonding property, rigidity, fluidity (moldability), and physical property balance of a thermoplastic resin composition, and a polybutylene terephthalate resin used in a typical thermoplastic resin composition can be used. For example, the polybutylene terephthalate resin can be obtained by polycondensation of terephthalic acid (TPA) or the like as a dicarboxylic acid component and 1,3-butanediol, 1,4-butanediol or the like as a diol component.

[0036] In a specific example, the polybutylene terephthalate resin of the present invention may have an intrinsic viscosity [η] measured according to ASTM D2857 of about 0.5 to about 1.5 dl / g, for example, about 0.7 to about 1.3 dl / g. Within this range, the mechanical properties, metal bonding properties, fluidity (moldability), etc. of the thermoplastic resin composition may be excellent.

[0037]

[0038] (B) Polycarbonate resin

[0039] According to one specific example of the present invention, a polycarbonate resin can be applied together with polybutylene terephthalate resin, specific glass fiber, etc. to improve the metal bonding property, rigidity, fluidity (moldability), and physical property balance of a thermoplastic resin composition, and a polycarbonate resin used in a typical thermoplastic resin composition can be used. For example, an aromatic polycarbonate resin produced by reacting a diphenol (aromatic diol compound) with a precursor such as phosgene, halogen formate, or carbonic diester can be used.

[0040] In specific examples, the diphenols may include, but are not limited to, 4,4'-biphenol, 2,2-bis(4-hydroxyphenyl)propane, 2,4-bis(4-hydroxyphenyl)-2-methylbutane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 2,2-bis(3-chloro-4-hydroxyphenyl)propane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, etc. For example, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane or 1,1-bis(4-hydroxyphenyl)cyclohexane can be used, and specifically, 2,2-bis(4-hydroxyphenyl)propane, also called bisphenol-A, can be used.

[0041] In a specific example, the polycarbonate resin may be one having a branched chain, and for example, a branched polycarbonate resin may be used that is prepared by adding about 0.05 to about 2 mol% of a trivalent or higher polyfunctional compound, specifically, a compound having a trivalent or higher phenol group, to the total diphenols used in the polymerization.

[0042] In specific examples, the polycarbonate resin may be used in the form of a homopolycarbonate resin, a copolycarbonate resin, or a blend thereof. In addition, the polycarbonate resin may be partially or entirely replaced with an aromatic polyester-carbonate resin obtained by polymerization in the presence of an ester precursor, such as a difunctional carboxylic acid.

[0043] In a specific example, the polycarbonate resin may have a weight average molecular weight (Mw) measured by gel permeation chromatography (GPC) of about 10,000 to about 50,000 g / mol, for example, about 15,000 to about 40,000 g / mol. Within this range, the thermoplastic resin composition may have excellent impact resistance, fluidity (moldability), etc.

[0044] In a specific example, the polycarbonate resin may be included in an amount of about 10 to about 40 parts by weight, for example, about 15 to about 35 parts by weight, and specifically about 15 to about 30 parts by weight, relative to about 100 parts by weight of the polybutylene terephthalate resin. If the content of the polycarbonate resin is less than about 10 parts by weight relative to about 100 parts by weight of the polybutylene terephthalate resin, there is a concern that the metal bonding properties of the thermoplastic resin composition may be reduced, and if it exceeds about 40 parts by weight, there is a concern that the rigidity, fluidity, etc. of the thermoplastic resin composition may be reduced.

[0045]

[0046] (C) Glass fiber

[0047] The glass fiber of the present invention can be applied together with polybutylene terephthalate resin, polycarbonate resin, etc. to improve the metal bonding property, rigidity, fluidity (moldability), and physical property balance of a thermoplastic resin composition, and glass fiber having an A value of about 30 to about 110 in the following formula 1 can be used.

[0048] [Formula 1]

[0049] A = (M × C) / 100

[0050] In the above formula 1, M is the magnesium (Mg) content value of the glass fiber (unit: ppm), and C is the content value of the surface treatment material among 100 wt% of the total glass fiber (unit: wt%).

[0051] Here, the magnesium content of the glass fiber can be measured by removing the surface treatment material using Ultra-wave (Acid: 3 mL HNO3 + 1 mL H2SO4 + 1 ml HF) and then performing inorganic quantitative analysis using ICP-OES, and the surface treatment material content of the glass fiber can be obtained from the reduced mass after heating the glass fiber at 750°C for 2 hours.

[0052] In a specific example, the glass fiber may have an A value of the above formula 1 of about 30 to about 110, for example, about 40 to about 90. When the A value of the above formula 1 is less than about 30, there is a concern that the metal bonding property, fluidity, etc. of the thermoplastic resin composition may be reduced, and when it exceeds about 110, there is a concern that the fluidity, etc. of the thermoplastic resin composition may be reduced.

[0053] In a specific example, the magnesium content of the glass fiber may be from about 4,000 to about 10,000 ppm, for example from about 5,000 to about 9,000 ppm. Within this range, the thermoplastic resin composition may exhibit excellent metal bonding properties, rigidity, fluidity, and the like.

[0054] In a specific example, the surface treatment material of the glass fiber may be a surface treatment agent (sizing agent) applied to ordinary glass fiber. The surface treatment agent may include, but is not limited to, a silane compound, a urethane compound, an epoxy compound, etc.

[0055] In a specific example, the content of the surface treatment material of the glass fiber may be about 0.1 to about 1.2 wt%, for example, about 0.2 to about 1.1 wt%, based on 100 wt% of the total glass fiber. Within this range, the metal bonding properties, rigidity, fluidity, etc. of the thermoplastic resin composition may be excellent.

[0056] In specific embodiments, the glass fibers may be in the form of fibers and may have various cross-sections such as circular, oval, rectangular, etc. For example, it may be preferable in terms of mechanical properties to use fibrous glass fibers having circular and / or rectangular cross-sections.

[0057] In a specific example, the glass fiber having a circular cross-section may have a cross-sectional diameter of about 5 to about 20 ㎛ as measured using a Scanning Electron Microscope (SEM) and a length before processing of about 2 to about 20 mm, and the glass fiber having a rectangular (flat) cross-section may have a cross-sectional aspect ratio (major axis of the cross-section / minor axis of the cross-section) as measured using a Scanning Electron Microscope (SEM) of about 1.5 to about 10, a minor axis of about 2 to about 10 ㎛, and a length before processing of about 2 to about 20 mm. In the above range, the rigidity, moldability, etc. of the thermoplastic resin composition may be improved.

[0058] In a specific example, the glass fiber may be included in an amount of about 20 to about 110 parts by weight, for example, about 30 to about 100 parts by weight, and specifically about 40 to about 90 parts by weight, relative to about 100 parts by weight of the polybutylene terephthalate resin. If the content of the glass fiber is less than about 20 parts by weight relative to about 100 parts by weight of the polybutylene terephthalate resin, there is a concern that the rigidity, etc. of the thermoplastic resin composition may be reduced, and if it exceeds about 110 parts by weight, there is a concern that the fluidity, etc. of the thermoplastic resin composition may be reduced.

[0059] In a specific example, the weight ratio (B:C) of the polycarbonate resin and the glass fiber may be about 1:1 to about 1:7, for example, about 1:1.5 to about 1:6, specifically about 1:2 to about 1:5.5. In this range, the metal bonding property, rigidity, fluidity, etc. of the thermoplastic resin composition may be more excellent.

[0060]

[0061] A thermoplastic resin composition according to one specific embodiment of the present invention may further include additives included in conventional thermoplastic resin compositions. Examples of the additives include, but are not limited to, flame retardants, antioxidants, anti-drip agents, lubricants, release agents, nucleating agents, antistatic agents, stabilizers, and mixtures thereof. When the additives are used, the content thereof may be about 0.001 to about 40 parts by weight, for example, about 0.1 to about 10 parts by weight, based on about 100 parts by weight of the polybutylene terephthalate resin.

[0062]

[0063] A thermoplastic resin composition according to one specific example of the present invention may be in the form of pellets obtained by mixing the above components and melt-extruding them at about 240 to about 300°C, for example, about 260 to about 290°C, using a conventional twin-screw extruder.

[0064] In a specific example, the thermoplastic resin composition may have a metal bonding strength of about 30 to about 50 MPa, for example, about 35 to about 45 MPa, measured after insert injection molding an aluminum-based metal specimen of 1.2 cm × 4 cm × 0.3 cm in size and a thermoplastic resin composition specimen of 1.2 cm × 4 cm × 0.3 cm in size so that the 1.2 cm × 0.3 cm cross-sections of each specimen are bonded to each other in accordance with ISO 19095.

[0065] In a specific example, the thermoplastic resin composition has a tensile strength of about 1,350 to about 1,850 kgf / cm of a 3.2 mm thick specimen measured under conditions of 5 mm / min according to ASTM D638. 2 , for example, about 1,400 to about 1,800 kgf / cm 2 It could be.

[0066] In a specific example, the thermoplastic resin composition may have a spiral flow length of about 110 to about 130 mm, for example, about 113 to about 125 mm, measured after injection molding in a spiral-shaped mold having a width of 10 mm and a thickness of 1 mm under conditions of a molding temperature of 280°C, a mold temperature of 150°C, an injection pressure of 100 MPa, and an injection speed of 100 mm / s.

[0067]

[0068] The molded article according to the present invention is formed from the thermoplastic resin composition. The thermoplastic resin composition can be manufactured in the form of pellets, and the manufactured pellets can be manufactured into various molded articles (products) through various molding methods such as injection molding, extrusion molding, vacuum molding, and casting molding. Such molding methods are well known to those skilled in the art to which the present invention pertains. The molded article has excellent metal bonding properties, rigidity, fluidity (moldability), and a balance of these physical properties, and is therefore useful as interior and exterior materials for electronic devices, automobile interior and exterior materials, and portable electronic communication devices.

[0069]

[0070] A composite according to the present invention may include a plastic member formed from the thermoplastic resin composition; and a metal member in contact with the plastic member.

[0071] In a specific example, the plastic member and the metal member may be in direct contact without the use of an adhesive. For example, the plastic member and the metal member may be manufactured in an integrated form through insert injection molding.

[0072] In a specific example, the metal member may include one or more metals selected from the group consisting of aluminum, titanium, iron, and zinc.

[0073]

[0074] Hereinafter, the present invention will be described in more detail through examples; however, these examples are for the purpose of explanation only and should not be construed as limiting the present invention.

[0075]

[0076] Example

[0077] Below, the specifications of each component used in the examples and comparative examples are as follows.

[0078] (A) Polybutylene terephthalate resin

[0079] Polybutylene terephthalate resin (PBT, manufacturer: Shinkong Synthetic Fibers, product name: Shinite K006, intrinsic viscosity [η]: approximately 1.3 dl / g) was used.

[0080] (B) Polycarbonate resin

[0081] Bisphenol-A polycarbonate resin (PC, manufacturer: Lotte Chemical, weight average molecular weight: approximately 25,000 g / mol) was used.

[0082] (C) Glass fiber

[0083] (C1) Glass fiber (M: 6,706 ppm, C: 0.70 wt%) having an A value of approximately 47 in the following formula 1 was used.

[0084] [Formula 1]

[0085] A = (M × C) / 100

[0086] In the above formula 1, M is the magnesium (Mg) content value of the glass fiber (unit: ppm), and C is the content value of the surface treatment material among 100 wt% of the total glass fiber (unit: wt%).

[0087] (C2) Glass fiber (M: 6,396 ppm, C: 0.99 wt%) with an A value of approximately 63 in the above formula 1 was used.

[0088] (C3) Glass fiber (M: 3,275 ppm, C: 0.52 wt%) with an A value of approximately 17 in the above formula 1 was used.

[0089] (C4) Glass fiber (M: 15,941 ppm, C: 0.82 wt%) with an A value of approximately 131 in the above formula 1 was used.

[0090]

[0091] Examples 1 to 6 and Comparative Examples 1 to 6

[0092] Each of the above components was added in the amounts shown in Tables 1 and 2 below, and then extruded at about 280°C to produce pellets. The extrusion was performed using a twin-screw extruder with an L / D of 44 and a diameter of 45 mm. The produced pellets were dried at about 100°C for more than 4 hours, and then injection-molded using a 6 oz injection molding machine (molding temperature: about 270°C, mold temperature: about 150°C) to produce specimens. The physical properties of the produced specimens were evaluated using the following methods, and the results are shown in Tables 1 and 2 below.

[0093]

[0094] Method of measuring physical properties

[0095] (1) Metal bonding strength (unit: MPa): According to ISO 19095, the bonding strength was measured after bonding an aluminum-based metal specimen and a thermoplastic resin composition specimen through insert injection molding (injection temperature: 270℃, mold temperature: 150℃). Here, the metal specimen used was an aluminum-based metal specimen with Geo Nation's TRI surface treatment to facilitate bonding with the resin composition specimen. In addition, the metal and thermoplastic resin composition specimens used were 1.2 cm × 4 cm × 0.3 cm in size, and the bonding strength was measured by bonding the 1.2 cm × 0.3 cm cross-sections together.

[0096] (2) Tensile strength (unit: kgf / cm) 2): According to ASTM D638, the tensile strength of a 3.2 mm thick specimen was measured under the condition of 5 mm / min.

[0097] (3) Spiral flow length (unit: mm): The spiral flow length of the injection-molded specimen was measured after injection molding in a spiral-shaped mold with a width of 10 mm and a thickness of 1 mm under the conditions of a molding temperature of 280°C, a mold temperature of 150°C, an injection pressure of 100 MPa, and an injection speed of 100 mm / s.

[0098]

[0099] Example 123456 (A) (parts by weight) 100 100 100 100 100 100 (B) (parts by weight) 15 20 30 20 20 20 (C1) (parts by weight) 80 80 80 40 90- (C2) (parts by weight) ----- 80 (C3) (parts by weight) ------ (C4) (parts by weight) ------ Metal bonding strength (MPa) 36 37 43 36 37 39 Tensile strength (kgf / cm) 2 )1,6001,6501,5901,4301,7501,620Spiral flow length (mm)119121115123114115

[0100]

[0101] Comparative Example 123456 (A) (parts by weight) 100 100 100 100 100 100 (B) (parts by weight) 55 0 20 20 20 20 (C1) (parts by weight) 80 80 10 120 -- (C2) (parts by weight) -- -- (C3) (parts by weight) -- 80 -- (C4) (parts by weight) -- -- 80 Metal bonding strength (MPa) 234 137 38 2237 Tensile strength (kgf / cm) 2 )1,6601,3101,1801,8001,5901,550Spiral flow length (mm)115101128959591

[0102]

[0103] From the above results, it can be seen that the thermoplastic resin composition according to the present invention has excellent metal bonding properties (metal bonding force), rigidity (tensile strength), fluidity (spiral flow length), and a balance of these physical properties.

[0104] On the other hand, when the polycarbonate resin is applied in an amount less than the content range of the present invention (Comparative Example 1), it can be seen that the metal bonding properties of the thermoplastic resin composition are reduced, and when the polycarbonate resin is applied in an amount exceeding the content range of the present invention (Comparative Example 2), it can be seen that the rigidity, fluidity, etc. of the thermoplastic resin composition are reduced. When the glass fiber is applied in an amount less than the content range of the present invention (Comparative Example 3), it can be seen that the rigidity, etc. of the thermoplastic resin composition are reduced, and when the glass fiber is applied in an amount exceeding the content range of the present invention (Comparative Example 4), it can be seen that the fluidity, etc. of the thermoplastic resin composition are reduced.

[0105] In addition, when glass fiber (C3) having an A value of Formula 1 below the range of the present invention is applied instead of the glass fiber of the present invention (Comparative Example 5), it can be seen that the metal bonding property, fluidity, etc. of the thermoplastic resin composition are deteriorated, and when glass fiber (C4) having an A value of Formula 1 exceeding the range of the present invention is applied (Comparative Example 6), it can be seen that the fluidity, etc. of the thermoplastic resin composition are deteriorated.

[0106]

[0107] The present invention has been described with reference to exemplary embodiments. Those skilled in the art will appreciate that the present invention can be implemented in modified forms without departing from its essential characteristics. Therefore, the disclosed embodiments should be considered illustrative rather than limiting. The scope of the present invention is set forth in the claims, not the foregoing description, and all differences within the scope equivalent thereto should be construed as being encompassed by the present invention.

Claims

1. About 100 parts by weight of polybutylene terephthalate resin; About 10 to about 40 parts by weight of polycarbonate resin; and A thermoplastic resin composition characterized by comprising about 20 to about 100 parts by weight of glass fiber having an A value of about 30 to about 110 in the following formula 1: [Formula 1] A = (M × C) / 100 In the above formula 1, M is the magnesium (Mg) content value of the glass fiber (unit: ppm), and C is the content value of the surface treatment material among 100 wt% of the total glass fiber (unit: wt%).

2. A thermoplastic resin composition according to claim 1, wherein the polybutylene terephthalate resin has an intrinsic viscosity [η] of about 0.5 to about 1.5 dl / g as measured according to ASTM D2857.

3. A thermoplastic resin composition according to claim 1 or 2, wherein the polycarbonate resin has a weight average molecular weight of about 10,000 to about 50,000 g / mol as measured by GPC (gel permeation chromatography).

4. A thermoplastic resin composition according to any one of claims 1 to 3, characterized in that the weight ratio of the polycarbonate resin and the glass fiber is about 1:1 to about 1:

7.

5. A thermoplastic resin composition according to any one of claims 1 to 4, characterized in that the thermoplastic resin composition has a metal bonding strength of about 30 to about 50 MPa, measured after bonding an aluminum-based metal specimen of 1.2 cm × 4 cm × 0.3 cm in size and a thermoplastic resin composition specimen of 1.2 cm × 4 cm × 0.3 cm in size so that the 1.2 cm × 0.3 cm cross-sections of each specimen are bonded together through insert injection molding in accordance with ISO 19095.

6. In any one of the first to fifth clauses, the thermoplastic resin composition has a tensile strength of about 1,350 to about 1,850 kgf / cm of a 3.2 mm thick specimen measured under conditions of 5 mm / min according to ASTM D638. 2 A thermoplastic resin composition characterized by:

7. A thermoplastic resin composition according to any one of claims 1 to 6, characterized in that the spiral flow length of a specimen measured after injection molding in a spiral-shaped mold having a width of 10 mm and a thickness of 1 mm is about 110 to about 130 mm under the conditions of a molding temperature of 280°C, a mold temperature of 150°C, an injection pressure of 100 MPa, and an injection speed of 100 mm / s.

8. A molded product characterized by being formed from a thermoplastic resin composition according to any one of claims 1 to 7.

9. A plastic member formed from a thermoplastic resin composition according to any one of claims 1 to 7; and A composite material characterized by including a metal member in contact with the plastic member.

10. A composite material according to claim 9, characterized in that the metal member comprises at least one metal selected from the group consisting of aluminum, titanium, iron, and zinc.