Resin products for piping components

Abstract

To provide a resin product for a piping member that is employed as a component to be in contact with fluid in a piping member, and capable of suppressing occurrence of blisters (projections) on a liquid contact surface in use for a longer period of time compared to conventional arts.SOLUTION: A resin product for a piping member is composed of an injection-molded product of a resin composition contains a polyvinylidene fluoride-based resin as a main component, where the injection-molded product satisfies the following formula (1) with the tensile strength of a surface part defined as TS1 and the tensile strength of an internal part defined as TS2: TS2 / TS1≥0.85 ... (1).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a resin product for piping members, and more particularly to a resin product advantageously employed as a component part of a diaphragm valve used in piping for transporting fresh salt water, wet chlorine gas, or the like in an electrolysis plant. [Background technology]

[0002] Homopolymers of vinylidene fluoride and copolymers having structural units based on vinylidene fluoride (hereinafter, these are collectively referred to as polyvinylidene fluoride resins) have been used as industrial materials in various fields because of their excellent chemical resistance, corrosion resistance, heat resistance, weather resistance, mechanical strength, and ease of processing. For example, piping members such as valves and pipe joints, at least one of which is made of polyvinylidene fluoride resins, are installed and used in piping lines for fresh salt water, wet chlorine gas, etc. in electrolysis plants, which require excellent corrosion resistance, and are also used in piping lines in various other chemical plants, which require mechanical strength, heat resistance, chemical resistance, etc. In addition, since polyvinylidene fluoride resins are generally thermoplastic and easy to process, the above-mentioned valves and pipe joints are often manufactured according to an injection molding method.

[0003] Although polyvinylidene fluoride resin has the above-mentioned excellent properties, it is known that in a diaphragm valve in which a resin product formed using polyvinylidene fluoride resin is used as a member that comes into contact with liquid, protrusions are formed on the liquid-contacting surface of the resin product after long-term use. Specifically, when a diaphragm valve having a valve body with a liquid flow path formed of polyvinylidene fluoride resin is installed and used in a piping line that conveys fresh salt water at 80 to 90°C, protrusions are generated on the surface of the flow path of the polyvinylidene fluoride resin valve body (especially the surface of the bent part) after 2 to 3 years from the start of use, and if the valve body continues to be used after the generation, the number of protrusions gradually increases, and the protrusions are connected to each other, promoting peeling of the resin on the surface of the valve body, and finally, a problem occurs in that the peeled resin is mixed into the fresh salt water flowing in the piping line. In this specification, the phenomenon in which protrusions are generated as described above will be referred to as the blister phenomenon, and the generated protrusions will be referred to as blisters.

[0004] In order to solve such problems, the applicant of the present application has proposed in Patent Document 1 (JP Patent Publication No. 10-281309) a polyvinylidene fluoride piping component having stress cracking resistance improved by more than two times compared to conventional components.

[0005] However, upon further investigation by the present inventors into the polyvinylidene fluoride piping component disclosed in Patent Document 1, it was found that, although the piping component disclosed in the document is capable of suppressing the occurrence of blisters to a certain degree, in recent years there has been an increasing need for piping components in which the occurrence of blisters can be suppressed for a longer period of time than before, and that in this regard there is still room for improvement. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-281309 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in light of the above circumstances, and the problem to be solved is to provide a resin product for piping members that, when used as a component that comes into contact with a fluid, can suppress the occurrence of blisters (protrusions) on the liquid-contacting surface for a longer period of time than conventional products. Another problem to be solved by the present invention is to provide a diaphragm valve equipped with such a resin product. [Means for solving the problem]

[0008] In order to solve such problems, the present invention provides an injection molded article made of a resin composition containing polyvinylidene fluoride resin as a main component. The resin product for a piping member is characterized in that the resin composition contains flavanthrone as a crystal nucleating agent in a proportion of 200 to 4000 ppm by mass. The gist of the present invention is a resin product for piping components, characterized in that the tensile strength TS1 of the surface portion of the injection-molded product and the tensile strength TS2 of the interior of the injection-molded product satisfy the following formula (1). TS2 / TS1≧ 0.86 ...Equation (1) (Note that TS1 in the above formula (1) is measured using sample I cut out from the surface of the injection-molded product in a shape such that the tensile direction in the tensile test is perpendicular to the thickness direction of the injection-molded product. Also, TS2 in the above formula (1) is measured using sample II cut out from the surface exposed after removing a thickness of 2 mm from the injection-molded product directly below the portion removed as sample I in the injection-molded product in a shape such that the tensile direction in the tensile test is perpendicular to the thickness direction of the injection-molded product.)

[0010] On the other hand, the present invention is Tree The present invention also relates to a diaphragm valve equipped with a grease product. Effect of the Invention

[0011] Thus, the resin product for piping members according to the present invention is an injection molded product obtained by using a resin composition mainly composed of a polyvinylidene fluoride resin as a molding material, and is constituted by a product in which the tensile strength of the surface portion and the tensile strength of the inside satisfy a predetermined relationship. Therefore, for example, when the resin product according to the present invention is used as a valve body having a flow path in contact with fresh salt water, etc., in a diaphragm valve used in a conveying pipe for fresh salt water, wet chlorine gas, etc. in an electrolytic plant, the occurrence of blisters (protrusions) on the liquid-contacting surface of the valve body to which the present invention is applied is suppressed for a longer period of time compared to conventional resin products, and thus the life of the diaphragm valve can be advantageously extended. [Brief description of the drawings]

[0012] [Figure 1] FIG. 2 is an explanatory diagram showing an outline of a process for preparing a sample to be used for measuring tensile strength. [Diagram 2] 1 is a longitudinal sectional view illustrating an embodiment of a diaphragm valve to which the present invention is applied. FIG. [Diagram 3] In the valve bodies according to the examples and the comparative examples, samples for measuring tensile strength were processed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described in detail below with reference to the drawings as appropriate.

[0014] The resin product for piping components according to the present invention (hereinafter also referred to simply as the resin product) is an injection-molded product obtained using a resin composition whose main component is a polyvinylidene fluoride resin, and is configured such that the tensile strength (tensile strength): TS1 of its surface portion and the tensile strength (tensile strength): TS2 of its interior portion satisfy the following formula (1). TS2 / TS1≧0.85...Equation (1)

[0015] The inventors have not yet fully understood the detailed principle behind the phenomenon whereby protrusions (blisters) form on the liquid-contacting surface of a polyvinylidene fluoride resin product when the resin product is in contact with a fluid such as fresh salt water for an extended period of time. However, the inventors have discovered that, among injection-molded products obtained using a resin composition whose main component is a polyvinylidene fluoride resin, particularly those in which the surface tensile strength: TS1 and the internal tensile strength: TS2 satisfy a specified relationship (the relationship of formula (1) above), the particle diameters of the crystals that make up the surface and the internal parts of the molded product are relatively uniform, and the occurrence of blisters can be suppressed for a longer period of time than in conventional products, and have completed the present invention.

[0016] Here, in the present invention, the tensile strength (TS1) of the surface part and the strength (TS2) of the inside of the injection molded product refer to the tensile strengths measured using each sample (sample I, sample II) prepared from the part shown in FIG. 1. Specifically, the tensile strength of the surface part: TS1 is measured using sample I (see FIG. 1(a)) cut out from the surface of the injection molded product in a shape such that the tensile direction of the tensile test is perpendicular to the thickness direction of the injection molded product. On the other hand, the tensile strength of the inside: TS2 is measured using sample II (see FIG. 1(c)) cut out from the surface exposed after the removal, in a shape such that the tensile direction of the tensile test is perpendicular to the thickness direction of the injection molded product, by removing a part of the injection molded product directly below the part removed as sample I over a thickness of 2 mm (see the cut part shown in FIG. 1(b)). Both TS1 and TS2 are measured according to the conditions and methods specified in JIS-K-7161:2014 "Plastics - Determination of tensile properties - Part 1." It should be understood that although Figures 1(a) to (c) show the longitudinal section of an injection-molded product (a section that appears when an injection-molded product is cut on a plane horizontal to its thickness direction), hatching has been omitted for convenience of explanation.

[0017] The resin product according to the present invention is an injection molded product obtained using a resin composition mainly composed of a polyvinylidene fluoride resin, and as the polyvinylidene fluoride resin used in producing the resin product of the present invention, any conventionally known polyvinylidene fluoride resin can be used as long as it is possible to produce a molded product (resin product) in which the surface tensile strength: TS1 and the internal tensile strength: TS2 satisfy a predetermined relationship by an injection molding method. Note that the polyvinylidene fluoride resin in the present invention includes not only vinylidene fluoride homopolymers, but also copolymers containing vinylidene fluoride units as structural units.

[0018] In producing the resin product of the present invention, a resin composition containing the polyvinylidene fluoride resin as the main component is used, and flavanthrone is advantageously added to the resin composition as a crystal nucleating agent. In an injection molded product (resin product) obtained using a resin composition containing flavanthrone, the crystal particles become uniformly fine, and the effect of the present invention that the occurrence of blisters (protrusions) can be more advantageously enjoyed. In addition, since the crystal particles in the injection molded product (resin product) become uniformly fine by the addition of flavanthrone, it is considered that the addition of flavanthrone also contributes to the reduction of dimensional changes of the product after long-term use. Note that flavanthrone is a compound that has been known as a yellow vat dye, and has tautomers as represented by the following formula (I). [ka]

[0019] When using the above-mentioned flavanthrone in the manufacture of the resin product according to the present invention, it is preferable to use the flavanthrone in an amount such that the content in the resin composition mainly composed of polyvinylidene fluoride resin is 200 to 4000 ppm by mass, preferably 500 to 2000 ppm by mass. If the content of flavanthrone in the resin composition is less than 200 ppm, there is a risk that the effect of blending flavanthrone cannot be advantageously enjoyed. On the other hand, even if the content of flavanthrone is more than 4000 ppm, the effect aimed at by the present invention is not significantly improved according to the amount used, and the yellowness of the injection molded product (resin product) is merely increased, so that from the viewpoint of cost-effectiveness, it is not advisable to use the flavanthrone in an amount more than 4000 ppm.

[0020] In addition, the resin composition used in producing the resin product according to the present invention can contain various conventionally known additives, such as fillers and reinforcing agents, in addition to the above-mentioned flavanthrone, as appropriate, so long as they do not impede the objectives of the present invention.

[0021] When the resin product of the present invention is manufactured by injection molding using the resin composition mainly composed of the polyvinylidene fluoride resin described above, the resin composition (molding material) is prepared according to the same method as in the past. For example, when using a polyvinylidene fluoride resin and a flavanthrone, the resin composition (molding material) is prepared according to the following method: 1) mixing the polyvinylidene fluoride resin and the like using a mixer such as a V-type blender, a ribbon blender, or a Henschel mixer; 2) melt-kneading the polyvinylidene fluoride resin and the like using a kneader such as an extruder, a mixing roll, a Banbury mixer, or a kneader; 3) mixing and kneading the above-mentioned mixer and kneader in combination; or 4) melt-kneading the polyvinylidene fluoride resin and the flavanthrone using the above-mentioned kneader to prepare a master batch, and mixing the master batch and the polyvinylidene fluoride resin, etc., to prepare the resin composition as the molding material. When the resin product according to the present invention is produced using only a polyvinylidene fluoride resin, it is not necessarily necessary to employ the above-mentioned step of preparing the resin composition (molding material).

[0022] Then, the prepared resin composition (molding material) is used to carry out injection molding according to a conventionally known injection molding method, thereby obtaining an injection-molded product, which is a resin product according to the present invention. Various molding conditions when carrying out such injection molding, such as molding temperature (cylinder temperature) and molding pressure (injection pressure), are appropriately determined according to the type of polyvinylidene fluoride resin used and the shape and size of the intended injection-molded product (resin product) so that an injection-molded product in which the tensile strength (TS1) of the surface portion and the tensile strength (TS2) of the interior satisfy the relationship of the present invention can be obtained. For example, a temperature in the range of 170 to 230°C is adopted as the molding temperature (cylinder temperature). If the molding temperature (cylinder temperature) is less than 170°C, there is a risk that a molded product cannot be manufactured according to the injection molding method, while if the temperature exceeds 230°C, it becomes difficult to obtain an injection-molded product in which the tensile strength (TS1) of the surface portion and the tensile strength (TS2) of the interior satisfy the relationship of the present invention. The molding pressure (injection pressure) is preferably set within the range of 35 to 65 MPa. At a molding pressure (injection pressure) exceeding 65 MPa, it is difficult to achieve uniform crystallization, and there is a risk of the strength of the molded product decreasing due to residual stress, etc., while at a molding pressure (injection pressure) below 35 MPa, there are problems such as the risk of insufficient filling of the molding material in the mold and the tendency to molding defects such as flow marks on the surface of the molded product.

[0023] The resin product according to the present invention is used as a conventionally known piping member or as one of the components constituting a piping member. Examples of piping members to which the present invention can be applied include various valves such as diaphragm valves, butterfly valves, control valves, and check valves, and pipe joints such as bends, elbows, and tees. Among these various piping members, the present invention is particularly advantageously applied to the valve body (valve body) of a diaphragm valve and the valve body of a butterfly valve.

[0024] Fig. 2 is a longitudinal cross-sectional explanatory view showing an example of a diaphragm valve using a resin product according to the present invention as a valve body, and Fig. 3 is a plan view showing the valve body. As is clear from Figs. 2 and 3, the diaphragm valve 10 has an inlet flow path 14 and an outlet flow path 16, and further has a partition wall 18 located between the flow paths 14, 16 and curving the flow paths, and has a valve body 12 in which a tip surface (upper surface) of the partition wall 18 serves as a valve seat 20. A bonnet 22 is attached so as to cover an opening formed above the partition wall 18 of the valve body 12, and a spindle 24 supported by the bonnet 22 can be moved up and down (axially) by rotating a handle 26. The diaphragm 30, which has a circular planar shape and is attached at its center to the compressor 28 fixed to the lower end of the spindle 24 and is movable and deformed in the vertical direction, is sandwiched at its periphery between the opening periphery of the valve body 12 and the lower end of the bonnet 22, thereby closing the opening of the valve body 12, while the center of the diaphragm 30 is pressed against or separated from the valve seat 20 by the vertical movement of the spindle 24 and thus the vertical movement of the compressor 28, thereby blocking or allowing the flow of liquid through the flow paths 14, 16. As for the driving method of the compressor 28 in the diaphragm valve 10, instead of the manual rotation of the handle 26 described above, a pneumatic driving method using air pressure or an electric driving method using a motor or the like can be adopted, and a known driving method will be appropriately adopted as the driving method.

[0025] Furthermore, when a diaphragm valve 10 using the resin product of the present invention as the valve body 12 as described above is arranged, for example, in a fresh / salt water piping line and used, with conventional products, after a certain period of time has passed since the start of use, the occurrence of blisters (protrusions) was observed on the wall surfaces of the parts of the valve body where the flow passages are bent (in the valve body 12, the wall surfaces near the partition wall 18 in the inlet flow passage 14 and outlet flow passage 16). However, with the valve body 12 which is the resin product of the present invention, the occurrence of blisters can be suppressed for a longer period of time than with conventional products, which greatly contributes to extending the life of the diaphragm valve 10. EXAMPLES

[0026] The present invention will be described in more detail below by showing some examples of the present invention, but it goes without saying that the present invention is not limited in any way by the description of such examples. It should be understood that the present invention can be modified, altered, improved, etc., based on the knowledge of a person skilled in the art, in addition to the following examples and the above specific description, without departing from the spirit of the present invention.

[0027] -Preparation of resin composition- First, a predetermined amount of polyvinylidene fluoride resin (Kureha Corporation, product name: Kureha KF Polymer #1000, melting point: 173°C) and an amount of flavanthrone such that the total amount of the polyvinylidene fluoride resin was 5000 ppm by mass were prepared. After mixing the polyvinylidene fluoride resin and the flavanthrone, the mixture was melt-kneaded and extruded at 230°C using an extruder to prepare flavanthrone-containing resin pellets (diameter: about 2 mm x length: 3 mm). Meanwhile, the polyvinylidene fluoride resin alone was melted and extruded using an extruder to prepare resin pellets (diameter: about 2 mm x length: 3 mm).

[0028] Then, 20 parts by mass of the flavanthrone-containing resin pellets were added to 80 parts by mass of the resin pellets and mixed to prepare a resin composition as a molding material. Note that the content of flavanthrone in this resin composition was 1000 ppm by mass.

[0029] -Manufacture of diaphragm valve bodies- Using the resin composition prepared as described above, a known injection molding method was carried out at the molding temperature (cylinder temperature) and molding pressure (injection pressure) shown in Table 1 below, to produce five types of diaphragm valve bodies for a caliber of 50A having the structures shown in Figs. 2 and 3 (Examples 1 to 4, Comparative Example 1).

[0030] -Measurement of tensile strength- A sample for measuring the "tensile strength of the surface" (sample I) and a sample for measuring the "tensile strength of the inside" (sample II) were cut out from the tip surface (top surface) of the partition wall of the manufactured valve body (see the sample cut-out area in Figure 3), and the tensile strength of each sample was measured according to the conditions and methods specified in JIS-K-7161:2014 "Plastics - Determination of tensile properties - Part 1", and the value of the inside tensile strength (TS2) / surface tensile strength (TS1) was calculated. The measurement results and calculation results are shown in Table 1 below.

[0031] -Implementation test- Each of the valve bodies according to the examples and the comparative examples was mounted on a diaphragm valve as shown in FIG. 2, and the diaphragm valve was installed on an electrolytic cell fresh salt water line (fluid: salt water, temperature: 80°C (normal use), pressure: almost no pressure (natural flow at electrolytic cell outlet), valve opening and closing frequency: once a year, piping installation location: indoors) in an electrolytic factory of a certain company, and operated for seven years. After seven years of use, the diaphragm valve was disassembled and the valve body was removed, and the presence or absence of blisters (protrusions) on the wall surface of the flow path of the valve body was visually observed. If no blisters were observed, it was evaluated as ○, and if blisters were observed, it was evaluated as ×. The evaluation of each valve body according to the examples and the comparative examples is also shown in Table 1 below.

[0032] [Table 1]

[0033] As is clear from the results in Table 1, in the valve body made of the resin product according to the present invention, no blisters were observed on the wall surface of the flow path even after a long period of use spanning seven years. This confirms that when the resin product of the present invention is used as the valve body of a diaphragm valve, it can greatly contribute to extending the service life of the diaphragm valve. [Explanation of symbols]

[0034] 10 Diaphragm Valve 12 Valve body 14 Inlet channel 16 Outlet flow path 18 Partition Wall 20 Valve seat

Claims

1. A resin product for piping members, which is an injection-molded product of a resin composition mainly composed of a polyvinylidene fluoride resin, The resin composition contains flavanthrone as a crystal nucleating agent in an amount of 200 to 4000 ppm by mass, The tensile strength of the surface portion of the injection molded product: TS1 and the tensile strength of the inside of the injection molded product: TS2 satisfy the following formula (1), A resin product for use as a piping member. TS2 / TS1≧0.86...Formula (1) (However, TS1 in the above formula (1) is measured using a sample I cut out from the surface of the injection-molded product in a shape such that the tensile direction in the tensile test is perpendicular to the thickness direction of the injection-molded product. Also, TS2 in the above formula (1) is measured using a sample II cut out from the surface exposed after removing a thickness of 2 mm from the injection-molded product directly below the portion removed as sample I in the injection-molded product in a shape such that the tensile direction in the tensile test is perpendicular to the thickness direction of the injection-molded product.)

2. A diaphragm valve equipped with the resin product described in claim 1.

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