JP7628407B2 - Acidic liquid contact component and method for improving acidic liquid resistance of component - Google Patents

Description

The present invention relates to an acidic liquid contact member containing a polyacetal resin composition that has high resistance to acid components, and a method for improving the acidic liquid resistance of the member.

Since polyacetal resin compositions have excellent chemical resistance, molded articles made from polyacetal resin compositions are widely used as automobile parts. For example, they are used as large parts such as fuel delivery units, which are representative of fuel contact bodies such as fuel pump modules that come into direct contact with fuel oil.

In recent years, fuels have been reduced in sulfur content in order to comply with environmental regulations in various countries. However, because 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.

The applicant of the present application has reported that these issues can be significantly improved by incorporating alkaline earth metal oxides, polyalkylene glycols, and specific ester compounds into polyacetal resins (Patent Document 1). This has resulted in significant improvements, particularly for parts such as fuel delivery units that come into contact with high-sulfur fuels.

Patent No. 5814419

Although automotive parts such as fuel delivery units are covered by a hood or other housing, splashes of detergent may adhere to them when washing the car. In particular, when removing brake dust and other particles that have adhered to the wheels, detergents with higher acidity than those used in high-sulfur fuels may be used, and the deterioration of automotive parts made of polyacetal resin due to these detergents is also a major issue.

The composition described in Patent Document 1 cannot adequately address these issues. By using an excess amount of alkaline earth metal oxide, it is possible to suppress deterioration caused by strong acidic cleaning agents, but at the same time, decomposition of unstable terminals in the polyacetal resin is promoted, which has an undesirable effect on mechanical properties, moldability, etc.

The present invention aims to provide an acidic liquid contact component containing a polyacetal resin composition that, when molded, can suppress deterioration when in contact with an acidic liquid such as an acidic cleaning agent.

As a result of extensive research to solve the above problems, the inventors discovered that by giving the polyacetal resin composition a specific composition, it is possible to minimize the deterioration that occurs when the molded product comes into contact with an acidic liquid.

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

The object of the present invention has been achieved by the following.
1. At least, relative to 100 parts by mass of the polyacetal polymer (A),
(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 less,
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.

The present invention provides a component obtained using a polyacetal composition that can minimize deterioration when in contact with an acidic liquid.

In the present invention, "acidic liquid" refers to a solution with 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.

Specific embodiments of the present invention are described in detail below, but the present invention is not limited to the following embodiments and can be modified as appropriate within the scope of the invention.

<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.

The composition of the polyacetal resin composition of the present invention is described in detail below.

<(A) Polyacetal polymer>
The polyacetal polymer (A) used in the present invention may be a homopolymer having an oxymethylene group (-OCH ₂ -) as a constituent unit (for example, "Delrin", a product name of DuPont, USA), or a copolymer having other comonomer units in addition to the oxymethylene unit (for example, "Duracon", a product name of Polyplastics Co., Ltd.). From the viewpoint of thermal stability, etc., a copolymer (hereinafter also referred to as a polyacetal copolymer) is preferable.

They are generally produced by copolymerizing formaldehyde or a cyclic compound of formaldehyde as the main monomer with a compound selected from cyclic ethers and cyclic formals as the comonomer, and are usually stabilized by removing unstable terminal portions through thermal decomposition, (alkali) hydrolysis, etc.

In particular, trioxane, a cyclic trimer of formaldehyde, is commonly 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 purified by methods such as distillation before use. It is preferable that the trioxane used in the polymerization contains as little impurities as possible, such as water, methanol, and formic acid.

As comonomers, general cyclic ethers and cyclic formals, as well as glycidyl ether compounds capable of forming branched or crosslinked structures, can be used alone or in combination of two or more.

The polyacetal copolymers described above can generally be obtained by adding an appropriate amount of molecular weight regulator and carrying out cationic polymerization using a cationic polymerization catalyst. The molecular weight regulators, cationic polymerization catalysts, polymerization methods, polymerization apparatuses, catalyst deactivation treatments after polymerization, and terminal stabilization treatment methods for crude polyacetal copolymers obtained by polymerization that are used are all known in many publications, and basically any of them can be used.

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, it is preferable that the melt index (measured in accordance with ISO1133 at 190°C and a load of 2.16 kg), which is an index of the fluidity of the resin, is 0.1 to 100 g/10 min, and more preferably 0.5 to 80 g/10 min.

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 terminals is 0.5 mass % or less. Here, the hemiformal terminal group is represented by --OCH ₂ OH, and is also called a hydroxymethoxy group or a hemiacetal terminal group.

The amount of the hemiformal end group and the formyl end group can be determined by ¹ H-NMR measurement, and the specific measurement method can be found in the method described in JP-A-2001-11143.

The amount of unstable terminals refers to the amount of portions present at the terminals of the 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%) aqueous methanol 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 that has decomposed and dissolved in the resulting solution, and expressing the amount as a mass % relative to the polyacetal copolymer.

<(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.

In the present invention, at least one or more of these antioxidants may be used.

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 will the antioxidant properties, which are the original objective, be insufficient, but the resistance to acidic liquids, which is the objective of the present invention, will also be poor. If the blending amount of the (B) antioxidant is excessive, this will have an undesirable effect on the mechanical properties, moldability, etc. of the resin composition.

<(C) Polyamide resin having 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.

Commercially available products include Amilan CM6241 (mp 190°C), Amilan CM4000 (mp 155°C), and 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), and AMINOTLDPA12 (mp 178°C) (all manufactured by Arkema), and Elvamide 8061 and 8063 (all manufactured by DuPont).

The melting point of the polyamide resin is 210°C or less, preferably 130°C to 200°C, from the viewpoint of dispersibility in the polyacetal resin. As long as it is within this range, there are no particular limitations on the composition of the polyamide.

In the present invention, the content of polyamide having a melting point of 210°C or less is 5.0 to 40 parts by mass, and more preferably 7 to 30 parts by mass, per 100 parts by mass of (A) polyacetal resin. 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 will be significantly reduced.

<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.

The polyacetal resin composition of the present invention may further contain one or more of heat stabilizers, weather (light) stabilizers, impact resistance improvers, gloss control agents, sliding improvers, fillers, colorants, nucleating agents, antistatic agents, surfactants, compatibilizers, etc., as necessary, so long as they do not impair the present invention.

<<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.

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.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

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)

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

(C) Polyamide (C-1) Elvamide 8063 (manufactured by DuPont) mp 158°C
(C-2) Amilan CM4000 (manufactured by Toray Industries, Inc.) mp 155°C
(C-3) Amilan CM8000 (manufactured by Toray Industries, Inc.) mp 137°C
(C-4) Eurelon 975 (Huntsman) mp 171-181°C
(C-5) Amilan CM1017 (manufactured by Toray Industries, Inc.) mp225°C
For (C-5), a powder obtained by freeze-pulverizing the pellets was added.

<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 pellet-shaped compositions.

<Evaluation>
(1) Evaluation of Acidic Liquid Resistance 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.

[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 following acidic liquid was dropped onto the surface of the apex of the curve of the tensile test piece (near the center in the longitudinal direction of the test piece), and the test piece was allowed to stand until cracks were generated at the part where the acidic liquid was dropped.
Acid liquid composition: 10% by weight aqueous solution of phosphoric acid

[Evaluation Criteria]
The time from the dropping of the acidic liquid to the occurrence of cracks on the test piece was classified as follows, from × 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

(2) Mechanical property evaluation Using the tensile test pieces molded in (1), the nominal tensile breaking strain at break was measured in accordance with ISO 527-1 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% or more but less than 10% ×: Less than 5%

As a result, the test pieces made of the polyacetal resin compositions of Examples 1 to 8 and Comparative Examples 3 and 5 did not develop cracks even after 15 hours or more, but the test pieces made of the polyacetal resin compositions of Comparative Examples 1, 2, 4, and 6 developed cracks within 15 hours.

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, but the test pieces made of the polyacetal resin compositions of Comparative Examples 3 and 5 had values lower than 5%.

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 (3)

( 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 . The acidic liquid contact member according to claim 1, wherein the (A) polyacetal polymer is an acetal copolymer. A method for improving the acidic liquid resistance of a component using the polyacetal resin composition according to claim 1 or 2.