Acidic liquid contact component and method for improving acidic liquid resistance of component

Abstract

To provide a polyacetal resin composition that, when made into a molding, can suppress degradation when in contact with acidic liquid such as an acidic detergent.SOLUTION: An acidic liquid contact member is obtained by using a polyacetal resin composition that at least contains, based on (A) a polyacetal polymer 100 pts.mass, (B) a hindered phenolic antioxidant 0.1-2.0 pts.mass, and (C) a polyamide with a melting point of 210°C or lower of 5.0-40 pts.mass.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an acidic liquid-contacting member containing a polyacetal resin composition having high resistance to acid components, and a method for improving the acidic liquid resistance of the member. [Background technology]

[0002] Since polyacetal resin compositions have excellent chemical resistance, molded articles made from the polyacetal resin compositions are widely used as automobile parts, for example, large parts such as fuel transport units, which are typified by fuel contact bodies such as fuel pump modules that come into direct contact with fuel oil.

[0003] In recent years, fuels have been reduced in sulfur content in order to comply with environmental regulations in various countries. However, since desulfurization equipment is very expensive, high-sulfur fuels are still in circulation in some countries. These high-sulfur fuels tend to deteriorate polyacetal resin compositions more easily than low-sulfur fuels.

[0004] The applicant of the present application has reported that these problems can be significantly improved by incorporating alkaline earth metal oxides, polyalkylene glycols, and specific ester compounds into polyacetal resins (Patent Document 1). This has been a major improvement, particularly for parts such as fuel delivery units that come into contact with high-sulfur fuels. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5814419 Summary of the Invention [Problem to be solved by the invention]

[0006] Although automobile parts such as fuel transport units are covered by a hood or other housing, splashes of detergent may adhere to them during car washing. In particular, when removing brake dust and other particles adhering to wheels, detergents with stronger acidity than high-sulfur fuels may be used, and the deterioration of automobile parts made of polyacetal resin due to these detergents is also a major issue.

[0007] The composition described in Patent Document 1 cannot fully address these issues. By using an excess amount of alkaline earth metal oxide, deterioration caused by a strong acid detergent can be suppressed, but at the same time, decomposition of unstable terminals in the polyacetal resin is promoted, and undesirable effects are observed on mechanical properties, moldability, etc.

[0008] An object of the present invention is to provide an acidic liquid contact member containing a polyacetal resin composition which, when molded into a molded product, is capable of suppressing deterioration when the molded product comes into contact with an acidic liquid such as an acidic cleaning agent. [Means for solving the problem]

[0009] Means for Solving the Problems The present inventors have conducted extensive research to solve the above problems and have discovered that by making a polyacetal resin composition into a specific composition, it is possible to minimize deterioration when a molded product comes into contact with an acidic liquid.

[0010] The inventors discovered that by using a composition containing polyamide, the above-mentioned undesirable effects can be suppressed to a practically acceptable range, and the ability to suppress deterioration when contacted with acidic liquids (hereinafter also referred to as acidic liquid resistance) can be significantly improved, and thus completed the present invention.

[0011] The object of the present invention has been achieved by the following. 1. At least (A) per 100 parts by mass of polyacetal polymer, (B) 0.1 to 2.0 parts by mass of a hindered phenol-based antioxidant, (C) 5.0 to 40 parts by mass of a polyamide having a melting point of 210° C. or lower, An acidic liquid contact member obtained using a polyacetal resin composition comprising: 2. The acidic liquid contact member according to 1 above, wherein the polyacetal polymer (A) is an acetal copolymer. 3. A method for improving the acidic liquid resistance of a member by using the polyacetal resin composition according to 1 or 2 above. Effect of the Invention

[0012] According to the present invention, it is possible to provide a member obtained by using a polyacetal composition that can minimize deterioration when in contact with an acidic liquid.

[0013] In the present invention, the term "acidic liquid" refers to a solution having a pH of 6 or less, and in some cases a pH of 2 or less, such as car detergents (car shampoos, wheel cleaners, etc.), household detergents (toilet cleaners, bathroom detergents, kitchen detergents, etc.), etc. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Specific embodiments of the present invention will be described in detail below. However, the present invention is not limited to the following embodiments and can be modified as appropriate within the scope of the object of the present invention.

[0015] <Polyacetal resin composition> The polyacetal resin composition used in the present invention comprises: The polyacetal resin composition is characterized in that it contains, relative to 100 parts by mass of (A) a polyacetal polymer, (B) 0.1 to 2.0 parts by mass of a hindered phenol-based antioxidant, and (C) 5.0 to 40 parts by mass of a polyamide having a melting point (hereinafter also referred to as mp) of 210°C or less.

[0016] The configuration of the polyacetal resin composition of the present invention will be described in detail below.

[0017] <(A) Polyacetal polymer> The polyacetal polymer (A) used in the present invention may be a homopolymer having an oxymethylene group (-OCH2-) as a constituent unit (e.g., DuPont, USA, trade name "Delrin" etc.), or a copolymer having other comonomer units in addition to the oxymethylene unit (e.g., Polyplastics Co., Ltd., trade name "Duracon" etc.). From the viewpoint of thermal stability, etc., it is preferable to use a copolymer (hereinafter also referred to as a polyacetal copolymer).

[0018] Generally, it is produced by copolymerizing formaldehyde or a cyclic compound of formaldehyde as the main monomer with a compound selected from cyclic ethers or cyclic formals as a comonomer, and is usually stabilized by removing unstable terminal moieties through thermal decomposition, (alkali) hydrolysis, etc.

[0019] In particular, trioxane, which is a cyclic trimer of formaldehyde, is generally used as the main monomer. Trioxane is generally obtained by reacting an aqueous solution of formaldehyde in the presence of an acid catalyst, and is used after being purified by a method such as distillation. It is preferable that the trioxane used in the polymerization contains as little impurities as possible, such as water, methanol, and formic acid.

[0020] As the comonomer, general cyclic ethers and cyclic formals, as well as glycidyl ether compounds capable of forming a branched structure or a crosslinked structure, can be used alone or in combination of two or more kinds.

[0021] The polyacetal copolymer as described above can generally be obtained by adding an appropriate amount of a molecular weight modifier and carrying out cationic polymerization using a cationic polymerization catalyst. The molecular weight modifier, cationic polymerization catalyst, polymerization method, polymerization apparatus, catalyst deactivation treatment after polymerization, and terminal stabilization treatment method for the crude polyacetal copolymer obtained by polymerization are known from many literatures, and basically any of them can be used.

[0022] The molecular weight of the polyacetal copolymer used in the present invention is not particularly limited, but it is preferable that the weight average molecular weight equivalent to polymethyl methacrylate determined by SEC (size exclusion chromatography) using 1,1,1,3,3,3-hexafluoroisopropanol as an eluent is 10,000 to 400,000. In addition, the melt index (measured according to ISO1133 at 190°C and a load of 2.16 kg), which is an index of the fluidity of the resin, is preferably 0.1 to 100 g / 10 min, more preferably 0.5 to 80 g / 10 min.

[0023] It is particularly preferred that the polyacetal polymer (A) used in the present invention has specific terminal characteristics. Specifically, the amount of hemiformal terminal groups is 1.0 mmol / kg or less, the amount of formyl terminal groups is 0.5 mmol / kg or less, and the amount of unstable terminal groups is 0.5 mass% or less. Here, the hemiformal terminal group is represented by -OCH2OH, and is also called a hydroxymethoxy group or a hemiacetal terminal group.

[0024] The formyl end group is represented by -OCHO. The amount of such hemiformal end groups and formyl end groups is 1 The specific measurement method can be found by H-NMR measurement, and the method described in JP-A No. 2001-11143 can be referred to.

[0025] The amount of unstable terminals refers to the amount of portions present at the terminals of a polyacetal polymer that are unstable to heat or bases and easily decompose. The amount of unstable terminals is determined by placing 1 g of polyacetal copolymer in a pressure-resistant sealed container together with 100 ml of a 50% (volume%) methanol aqueous solution containing 0.5% (volume%) ammonium hydroxide, heating the container at 180°C for 45 minutes, cooling the container, and opening the container to quantify the amount of formaldehyde decomposed and dissolved in the resulting solution, and expressing the amount as a mass % relative to the polyacetal copolymer.

[0026] <(B) Hindered phenol-based antioxidant> Examples of the hindered phenol-based antioxidant (B) used in the present invention include 2,2'-methylenebis(4-methyl-6-t-butylphenol), hexamethylene glycol-bis(3,5-di-t-butyl-4-hydroxyhydrocinnamate), pentaerythritol-tetrakis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, triethylene glycol-bis-3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxy-benzyl)benzene, n-octadecyl-3-(4'-hydrocinnamate), ... Examples include 4,4'-methylenebis(2,6-di-t-butylphenol), 4,4'-butylidene-bis(6-t-butyl-3-methyl-phenol), di-stearyl-3,5-di-t-butyl-4-hydroxybenzylphosphonate, 2-t-butyl-6-(3-t-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenyl acrylate, 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, and the like.

[0027] In the present invention, at least one or more kinds selected from these antioxidants can be used.

[0028] The content of the (B) hindered phenol-based antioxidant in the present invention is 0.1 to 2.0 parts by mass, and more preferably 0.2 to 1.5 parts by mass, per 100 parts by mass of the (A) polyacetal resin. If the blending amount of the (B) antioxidant is small, not only the antioxidant property, which is the original objective, becomes insufficient, but also the resistance to acidic liquids, which is the objective of the present invention, becomes poor. If the blending amount of the (B) antioxidant is excessive, it causes undesirable effects on the mechanical properties, moldability, etc. of the resin composition.

[0029] <(C) Polyamide resin with a melting point of 210°C or less> The polyamide resin (C) in the present invention is a resin having two or more amide bonds in the molecule, and examples thereof include copolymer polyamides such as polyamide 6-66, polyamide 6-66-10, polyamide 6-66-10-12, polyamide 11 (mp 185° C.), polyamide 12 (mp 175° C.), etc. These polyamide resins may be used alone or in combination of two or more. In the present invention, the melting point refers to a melting temperature measured in accordance with ISO11357-3.

[0030] Commercially available products include Amilan CM6241 (mp 190°C), Amilan CM4000 (mp 155°C), Amilan CM8000 (mp 137°C) (all manufactured by Toray Industries, Inc.), Hiprolon 200NNPA1010 (mp 202°C), Hiprolon 400NNPA1012 (mp 190°C), Rilsan BMNOPA11 (mp 189°C), AMNOTLDPA12 (mp 178°C) (all manufactured by Arkema), Elvamide 8061, Elvamide 8063 (all manufactured by DuPont), and the like.

[0031] From the viewpoint of dispersibility in the polyacetal resin, the melting point of the polyamide resin is 210° C. or less, preferably 130° C. to 200° C. As long as it is within this range, the composition of the polyamide is not particularly limited.

[0032] The content of the polyamide having a melting point of 210° C. or less in the present invention is 5.0 to 40 parts by mass, and more preferably 7 to 30 parts by mass, relative to 100 parts by mass of the polyacetal resin (A). If it is less than 5.0 parts by mass, the effect of acidic liquid resistance is insufficient, and if it exceeds 40 parts by mass, the mechanical properties are significantly reduced.

[0033] <Other ingredients> The polyacetal resin composition used in the present invention may contain known basic compounds, provided that such compounds do not impair the objects and effects of the present invention.

[0034] The polyacetal resin composition of the present invention may further contain, as necessary, one or more of a heat stabilizer, a weather (light) resistance stabilizer, an impact resistance improver, a gloss control agent, a sliding property improver, a filler, a colorant, a nucleating agent, an antistatic agent, a surfactant, a compatibilizer, and the like, provided that the invention is not impaired.

[0035] <<Parts obtained using polyacetal resin composition>> A member obtained using the polyacetal resin composition of the present invention can be used for automobile parts, such as automobile wheels, which may come into contact with cleaning agents when washing the vehicle body, or for other applications in which the member comes into contact with acidic liquids.

[0036] This member can be obtained by molding the polyacetal resin composition by a conventional molding method such as injection molding, extrusion molding, compression molding, blow molding, vacuum molding, foam molding, and rotational molding. The member of the present invention is prevented from deteriorating even when it comes into contact with a strongly acidic liquid having a pH of 2 or less, and can maintain a good surface appearance of the molded product. EXAMPLES

[0037] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these. There is none.

[0038] The various components in Tables 1 and 2 are as follows. The units in the tables are parts by mass. (A) Polyacetal polymer Polyacetal copolymer obtained by copolymerizing 96.7% by mass of trioxane and 3.3% by mass of 1,3-dioxolane (Melt index (measured in accordance with ISO1133 at 190°C and a load of 2.16 kg): 9 g / 10 min)

[0039] (B) Hindered phenol antioxidant (B-1) Pentaerythritol-tetrakis-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate (Irganox 1010, manufactured by BASF)

[0040] (C) Polyamide (C-1) Elvamide 8063 (DuPont) mp 158°C (C-2) Amilan CM4000 (Toray Industries, Inc.) mp155℃ (C-3) Amilan CM8000 (Toray Industries, Inc.) mp137℃ (C-4) Eurelon 975 (Huntsman) mp 171-181℃ (C-5) Amilan CM1017 (Toray Industries, Inc.) mp225℃ In addition, for (C-5), a powder obtained by freeze-pulverizing the pellets was added.

[0041] <Examples and Comparative Examples> The various components shown in Tables 1 and 2 were mixed in the ratios shown in Tables 1 and 2, and melt-kneaded in a twin-screw extruder to prepare a pellet-shaped composition.

[0042] <Evaluation> (1) Evaluation of resistance to acidic liquids Using the polyacetal resin compositions prepared in the Examples and Comparative Examples, ISO type 1-A tensile test pieces having a thickness of 4 mm were prepared by injection molding.

[0043] [Evaluation method] In order to evaluate the acidic liquid resistance of the polyacetal resin composition, both ends of the tensile test piece were fixed and curved to a bending strain of 1.5%. Under conditions of 23°C and 50%±10% RH, 10 μL of the acidic liquid described below was dropped onto the surface of the apex of the curve of the tensile test piece (near the center of the test piece in the longitudinal direction) and the test piece was left to stand until cracks appeared at the part where the acidic liquid was dropped. Acid liquid composition: 10% by weight phosphoric acid aqueous solution

[0044] [Evaluation Criteria] The time from when the acidic liquid was dropped to when cracks occurred on the test piece was classified as follows: × to ⊚. The results are shown in Tables 1 and 2. ◎: 30 hours or more ○: 15 hours or more but less than 30 hours △: 5 hours or more but less than 15 hours ×: Less than 5 hours

[0045] (2) Mechanical property evaluation Using the tensile test pieces molded in (1), the nominal tensile breaking strain at break was measured in accordance with ISO527-1 and 527-2. The atmosphere in the measurement room was maintained at 23°C and 50% RH. The nominal tensile breaking strain was classified as follows. The results are shown in Tables 1 and 2. ○: 10% or more △: 5% to less than 10% ×: Less than 5%

[0046] [Table 1]

[0047] [Table 2]

[0048] As a result, in the test pieces made of the polyacetal resin compositions of Examples 1 to 8 and Comparative Examples 3 and 5, no cracks occurred in the test pieces even after 15 hours or more, but in the test pieces made of the polyacetal resin compositions of Comparative Examples 1, 2, 4, and 6, cracks occurred in the test pieces within 15 hours.

[0049] In addition, the test pieces made of the polyacetal resin compositions of Examples 1 to 8 and Comparative Examples 1, 2, 4, and 6 had nominal tensile break strains of 5% or more, while the test pieces made of the polyacetal resin compositions of Comparative Examples 3 and 5 had values ​​lower than 5%.

[0050] From the Examples and Comparative Examples, it was confirmed that the product of the present invention is excellent in both acidic liquid resistance and mechanical properties.

Claims

1. (A) 100 parts by mass of a polyacetal polymer; (B) 0.1 to 2.0 parts by mass of a hindered phenol-based antioxidant; (C) 19 to 30 parts by mass of a polyamide resin having a melting point of 210° C. or less; The composition comprises A member for contacting an acidic liquid, obtained by using a polyacetal resin composition, the resin components of which are the polyacetal polymer and the polyamide resin.

2. 2. The acidic liquid contact member according to claim 1, wherein said polyacetal polymer (A) is an acetal copolymer.

3. A method for improving the acidic liquid resistance of a member by using the polyacetal resin composition according to claim 1 or 2.

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