JP6129715B2 - Lifetime estimation method for polyolefin material and method for manufacturing polyolefin tube - Google Patents

Description

  The present invention relates to a method for estimating the lifetime of a polyolefin material and a method for producing a polyolefin tube.

  Since plastic has advantages such as low cost, light weight, and high corrosion resistance as compared with metal, cases in which plastic material is applied to members that have conventionally used metal are increasing. In recent years, it has been studied to apply plastic materials such as polyethylene materials and polypropylene materials to members such as city gas supply piping and hot water transportation piping used in gas hot water systems.

  However, since plastic materials generally have low durability against ultraviolet rays and heat, when applied to piping, perform durability evaluation in advance to estimate the life that will be used as a guideline for renewal, It is desirable from the viewpoint of safety, cost, etc., to evaluate the degree of deterioration of the plastic tube and to estimate the remaining life. The following methods are known as methods for evaluating a member such as a plastic material and a tube formed using the plastic material.

For example, as a method for quickly evaluating the durability of a polyethylene resin gas pipe and determining the quality of the polyethylene resin for the gas pipe, the molecular weight distribution and branch density of the polyethylene resin are measured and the branch chain length is identified. There are known a method for evaluating the durability of a polyethylene resin gas pipe and a method for determining the quality of a polyethylene resin for a gas pipe, which are judged to have good durability when a specific condition is satisfied (see, for example, Patent Document 1).
In addition, as a method for easily and reliably evaluating the remaining life of a resin tube in a short period, the oxidation induction time of the resin tube in use is measured, and the remaining life of the resin tube is evaluated based on the measurement result. A method for diagnosing deterioration of a resin pipe is known (for example, see Patent Document 2).

JP-A-11-230962 Japanese Patent Laid-Open No. 2002-257819

  However, for example, in the case of a usage mode in which hot water is circulated through a pipe using propylene material, it is necessary to obtain detailed knowledge about how deterioration of the pipe progresses and how much life can be expected. The fact is that no suitable technology has been established.

  For example, hot water transport pipes molded from plastic materials (hereinafter referred to as hot water transport plastic pipes) are beginning to be examined not only indoors but also outdoors. Hot water transport plastic pipes transport relatively high-temperature fluids, so the physical properties and molecular structure change with time are larger than when used at room temperature. There is a risk. Therefore, it is assumed that the plastic pipe for transporting hot water used outdoors will have a shorter time until the expected performance cannot be exhibited, that is, the product life.

  The evaluation of the long-term durability of the plastic material may have to be performed in a short period of time in order to determine whether or not the used member itself can be continuously used. Generally, in order to determine whether or not a member can be used in a short period of time, it is necessary to perform a deterioration promotion test. When conducting such an accelerated test, the mechanism of deterioration differs depending on the usage environment and material type of the component to be evaluated. It is necessary to know in advance, for each material, whether acceleration is possible, what acceleration rate is possible when acceleration is possible.

2. Description of the Related Art In recent years, there is a solar heat collecting panel using a pipe made of polypropylene (hereinafter sometimes abbreviated as PP), which is a kind of polyolefin-based plastic, as a plastic pipe for hot water that has been studied for use outdoors. This panel is installed on the rooftop of a building, etc., so that solar heat is transferred to water circulating in the panel to make hot water, which is used for purposes such as hot water supply and heating residual heat.
It is known that polyolefin-based plastics generally undergo an oxidation reaction in a chain by radicals generated by ultraviolet rays or heat. In the case of PP, since it has a tertiary carbon from which hydrogen is easily extracted, radicals are easily generated, and deterioration progresses particularly quickly among polyolefin plastics. Therefore, when PP is used outdoors, many additives such as an antioxidant and an ultraviolet absorber are blended for the purpose of improving heat resistance and weather resistance. However, these additives are not only consumed with time, but also come into contact with the flowing water and flow into the water, so there is a concern that the durability may be significantly reduced by long-term use. In particular, in the case of a hot water pipe, since the temperature of the transport medium that circulates in the pipe is relatively high, it is assumed that the rate of decrease of the additive is increased compared to the case where the medium is at room temperature. Therefore, it is important to understand the decreasing behavior of the additive.

  For the evaluation of long-term durability of PP materials, there are reports of examining the temporal change behavior of tensile strength and the progress of oxidative degradation by irradiating ultraviolet rays for the purpose of evaluating weather resistance, but the effect of hot water is evaluated. There are no examples. In addition, for the purpose of evaluating long-term durability in a hot water environment, although there have been reports examining the temporal change behavior of the tensile strength of crosslinked polyethylene materials, the progress of oxidative degradation, and the remaining amount of additives, PP that is prone to oxidative degradation There have been no studies conducted on materials. For this reason, the degradation acceleration test method applicable to the evaluation of long-term durability of hot water PP pipes intended for outdoor use and the acceleration rate have not been clarified.

  The present invention has been made in view of the above circumstances, and is a polyolefin that simply estimates the life or remaining life of a polyolefin material used in a wetted environment (for example, an environment in contact with warm water (eg, 60 ° C. to 80 ° C.)). It is an object of the present invention to provide a method for estimating the life of a material, and a method for producing a polyolefin tube by which a life can be easily evaluated and a polyolefin tube having a desired quality can be stably obtained. .

  The present invention aims to establish a method for evaluating the long-term durability of PP pipes for hot water, etc., and compares the analysis results of physical properties and molecular structures of actually used members with the analysis results of unused members. We have obtained the knowledge that it is possible to estimate the life by clarifying the deterioration mechanism of the member, selecting the life evaluation index for evaluating the onset of deterioration, and determining the acceleration rate of deterioration. The present invention has been achieved based on this finding.

Specific means for solving the above-described problems are as follows.
<1> A method for estimating the lifetime of a polyolefin material containing an antioxidant,
The oxidation start temperature of the polyolefin material forming the used member is measured, and the obtained measurement value is calculated as the number of treatment days in the deterioration promotion treatment performed on the polyolefin material forming the unused member and the oxidation start temperature of the polyolefin material. Applying the above relationship to find the corresponding processing days,
Dividing the use days (use period) of the use member by the corresponding process days to calculate a deterioration promotion rate by the deterioration promotion process;
A polyolefin prepared based on the relationship between the number of treatment days in the deterioration accelerating treatment and the oxidation start temperature of the polyolefin material, and the relationship between the number of treatment days in the degradation accelerating treatment and the residual ratio of the antioxidant contained in the polyolefin material. An arbitrary point on the relationship line between the oxidation start temperature of the material and the remaining ratio of the antioxidant contained in the polyolefin material is defined as an index of the lifetime of the polyolefin material, and the deterioration acceleration rate is determined in the treatment days corresponding to the arbitrary point. To calculate the life of the polyolefin material,
It is the lifetime estimation method of the polyolefin material containing this.

  <2> The lifetime estimation method according to <1>, wherein the arbitrary point is a bending point on the relation line.

  <3> The lifetime estimation method according to <1> or <2>, wherein the polyolefin material is a polypropylene material.

  <4> In any one of the above items <1> to <3>, wherein the used member and the unused member are pipes for water circulation through which heated water (for example, hot water of 60 ° C. to 80 ° C.) flows. This is the life estimation method described.

  <5> The lifetime estimation method according to any one of <1> to <4>, wherein the oxidation start temperature is measured by differential scanning calorimetry.

  <6> The lifetime according to any one of <1> to <5>, wherein the deterioration accelerating treatment is a treatment of subjecting a polyolefin material to light irradiation using a xenon lamp as a light source and water spraying. Estimation method.

  <7> A step of selecting a polyolefin material having a lifetime estimated by the lifetime estimation method according to any one of <1> to <6> above a predetermined reference value, and using the selected polyolefin material A process for producing a polyolefin pipe, and a method for producing a polyolefin pipe.

In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In this specification, when referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, a plurality of substances present in the composition unless otherwise specified. Means the total amount.

  In this specification, the term “process” is not limited to an independent process, but is included in the term if the intended purpose of the process is achieved even if it cannot be clearly distinguished from other processes. It is.

ADVANTAGE OF THE INVENTION According to this invention, the lifetime estimation method of the polyolefin material which estimates simply the lifetime or residual lifetime of the polyolefin material used in a water contact environment (for example, the environment which contacts warm water (for example, 60 to 80 degreeC)) is provided. The Also,
ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the polyolefin pipe | tube which can perform the life evaluation simply and can obtain the polyolefin pipe | tube which has desired quality stably is provided.

It is IR spectrum obtained by carrying out infrared spectroscopy analysis of the use member and the deterioration promoting material. It is a graph which shows the relationship between the processing days in a deterioration promotion process, and the residual rate of the antioxidant contained in polyolefin material. It is a graph which shows the relationship between the number average molecular weight of a deterioration promotion sample, and the residual rate of antioxidant. It is a graph which shows the relationship between the process days in a deterioration promotion process, and the oxidation start temperature of polyolefin material. It is a graph which shows the relationship between the oxidation start temperature of polyolefin material in a deterioration promotion process, and the residual rate of the antioxidant contained in polyolefin material. It is a graph which shows the relationship between the process days in a deterioration promotion process, and the oxidation start temperature of polyolefin material. It is a figure which shows the shape of a test body used for the measurement of tensile strength, and a tensile direction.

  The polyolefin material life estimation method and polyolefin tube manufacturing method of the present invention will be described in detail below.

<Lifetime estimation method for polyolefin materials>
The polyolefin material lifetime estimation method of the present invention (hereinafter referred to as “life estimation method” as appropriate) is a lifetime estimation method for estimating the lifetime of a polyolefin material containing an antioxidant. Specifically, the life estimation method of the present invention includes at least the following steps (A) to (C).
Step (A): The oxidation start temperature of the polyolefin material forming the used member is measured, and the obtained measured value is treated with the treatment days and the polyolefin material in the deterioration promoting treatment performed on the polyolefin material forming the unused member. Step of obtaining the corresponding treatment days by applying to the relationship with the oxidation start temperature of step (B): The deterioration by dividing the use days (use period) of the used members by the “corresponding treatment days” Step of calculating the deterioration promotion rate by the acceleration treatment Step (C): Relationship between the number of treatment days in the deterioration acceleration treatment and the oxidation start temperature of the polyolefin material, and the number of treatment days in the deterioration acceleration treatment and the antioxidant contained in the polyolefin material The oxidation start temperature of the polyolefin material and the antioxidant contained in the polyolefin material were created based on the relationship with the residual ratio of the agent. Defines an arbitrary point relation line between the presence ratio as an indicator of the life of the polyolefin material, the processing number of days corresponding to the arbitrary point, by multiplying the deterioration promotion rate, calculating a lifetime of polyolefin material

Conventionally, it has been attempted to evaluate the long-term durability of a polyolefin from the viewpoint of the change over time of the tensile strength of a polyolefin material such as polyethylene, the progress of oxidative deterioration, and the residual ratio of additives such as antioxidants. . However, the degree of deterioration that progresses in various environments where polyolefin materials are used varies, and the useful life of polyolefin materials (so-called lifespan) and the remaining life of polyolefin materials used are estimated according to the environment of use. A simple method has not been proposed.
In the present invention, the use of a member using a polyolefin material such as polypropylene generally containing an antioxidant because it is prone to oxidative degradation, the use member calculated based on the theoretical number of days of unused member By associating the deterioration acceleration rate with an arbitrary point on the relationship line indicating the relationship between the oxidation start temperature of the polyolefin material and the residual ratio of the antioxidant contained in the polyolefin material, the polyolefin material The life or remaining life of the product is estimated. In particular, the life or remaining life (for example, the service life) of the polyolefin material is specifically estimated by obtaining the number of days of treatment at the bending point on the relationship line.

Hereafter, each process which comprises this invention is explained in full detail.
-Process (A)-
In the step (A) in the present invention, the oxidation start temperature of the polyolefin material forming the used member is measured, and the obtained measurement value is treated in the deterioration promoting process performed on the polyolefin material forming the unused member. By applying the relationship between the number of days and the oxidation start temperature of the polyolefin material, the corresponding number of treatment days is obtained.

In the present invention, the “used member” means a member that is actually used or used outdoors (for example, a hot water circulation pipe that is exposed to sunlight outdoors and in which hot water is circulated or distributed). Water distribution piping).
The “unused member” is a new member (for example, a water circulation pipe such as the hot water circulation pipe as described above) before being actually used.

  The oxidation start temperature (° C.) is a temperature at which the oxidation of the polyolefin material begins to proceed, and using a differential scanning calorimeter (DSC: Differential Scanning Calorimeter, STAR System DSC-30, manufactured by METTLER TOLEDO) It is a value obtained under conditions of a temperature increase rate of 10 ° C./min in an oxygen environment. In DSC, it can be regarded as the temperature indicating the starting point of the increase in heat quantity of the exothermic peak that appears due to oxidation when the temperature of the sample piece is raised at a predetermined rate.

  In this process, first, in order to obtain the theoretical number of days of treatment based on the oxidation start temperature obtained from the used member, when the deterioration promoting treatment is performed on the polyolefin material constituting the unused member. The relationship between the treatment days and the oxidation start temperature of each polyolefin material is obtained.

Specifically, it can be performed as follows.
First, a deterioration promoting process is performed on an unused polyolefin material. What is necessary is just to set arbitrarily the desired period in which a deterioration tendency appears for the period to implement.
Next, the oxidation start temperature is measured for each sample subjected to the deterioration promotion treatment using a differential scanning calorimeter (DSC) every predetermined period. Using the obtained measured value, the relationship between the number of treatment days and the oxidation start temperature is determined. Specifically, a relationship line (for example, a graph shown in FIG. 4) is created in which one axis (for example, the horizontal axis) is the number of processing days and the other axis (for example, the vertical axis) is the oxidation start temperature.

The deterioration promotion process may be performed by the following method, for example.
(1) Xenon light irradiation and water spray method (water spray xenon)
For an unused polyolefin material, irradiation time and irradiation intensity (for example, 60 W / m ^{2 to} 180 W / m ² (wavelength of 300 nm) with a xenon lamp (for example, a panel temperature of 50 ° C. to 95 ° C.) so as to obtain a desired integrated light amount. ˜400 nm)) is set and irradiation with xenon light is performed, and the operation (treatment 1) of jetting water during part or all of the irradiation time is repeated for a desired period.
In this case, a xenon weather meter manufactured by Suga Test Instruments Co., Ltd. can be used as the irradiation device. Moreover, you may perform irradiation on the following conditions, for example.
<Condition example>
・ Panel temperature: 63 ± 3 ℃
・ Irradiation time: Throughout the test period ・ Water spraying time: 18 minutes every 120 minutes of irradiation time Water is sprayed into a shower or mist using a liquid ejector such as a nozzle with a hole or an injector. This can be done by blowing out water.
(2) Method by Photothermal Water Cycle A series of treatments consisting of the above treatment 1 for 2 days, a heat treatment for holding in a constant temperature bath at 80 ° C. for 3 days, and a treatment for immersing in warm water (60 ° C.) for 2 days. One cycle is repeated as many times as desired.

Here, as an example, the following used members A and B, and the same unused polypropylene (PP) pipe (unused member) as used members A and B, 28 under the conditions (1) and (2) above. Infrared spectroscopic analysis was performed on the deterioration promoting material subjected to the treatment for one day, and the obtained IR spectrum is shown in FIG.
In addition, infrared spectroscopic analysis is to measure the surface of a product to be measured using a reflection infrared spectroscopic analyzer (FT-IR; Fourier Transform Infrared Spectroscopy) (Varian670 / 610-IR / Agilent, Technologies). It was done by.
-Use member A: PP pipe installed outdoors for 443 days and circulating hot water of about 60 ° C inside-Use member B: PP pipe installed outdoors for about 734 days and circulating hot water of about 60 ° C inside inside The used members A and B are the same polypropylene (PP) pipes as the “used products A and B” used in the examples described later.

As shown in FIG. 1, absorption (absorption at a wave number of 1730 cm ⁻¹ ) considered to be derived from a carbonyl group indicating the progress of oxidative deterioration of the polypropylene material is observed in all IR spectra of the used member and the deterioration promoting material. That is, it is considered that the deterioration promoting material treated under the conditions (1) and (2) reproduces substantially the same deterioration as the members A and B used.
In this way, it is possible to estimate the lifetime more suitably by performing the deterioration promoting process such that an absorption peak derived from a carbonyl group showing the progress of oxidation deterioration (absorption peak at a wave number of 1730 cm ⁻¹ ) appears. . Absorption at a wave number of 1730 cm ⁻¹ represents, for example, a change in the molecular structure that appears prominently in deterioration of the polypropylene material. For example, as an index of deterioration when performing deterioration promotion processing for estimating the life of a member using the polypropylene material Is preferred.

  Next, the oxidation start temperature of the used member is measured by the same method as described above. The measured oxidation start temperature is applied to the relationship line (relationship between the processing days of the deterioration promotion process and the oxidation start temperature) obtained from the deterioration promotion process of the unused member as described above. Thereby, the theoretical number of processing days (the number of processing days corresponding to the oxidation start temperature of the used member) corresponding to the oxidation start temperature of the used member is obtained.

-Process (B)-
In the step (B) in the present invention, the deterioration promotion rate by the deterioration promotion processing is calculated by dividing the usage days of the used members by the “corresponding processing days” obtained in the step (A).

In this step, the period of actual use of the used member (actual use day) is divided by the theoretical number of days of treatment corresponding to the oxidation start temperature of the used member, and the deterioration promotion rate by the deterioration promotion process is obtained.
Deterioration promotion rate = (actual use days) / (treatment days corresponding to oxidation start temperature of used parts)

-Process (C)-
In the step (C) of the present invention, an arbitrary point on the relationship line between the oxidation start temperature of the polyolefin material and the residual ratio of the antioxidant contained in the polyolefin material is defined as an index of the lifetime of the polyolefin material, The life of the polyolefin material is calculated by multiplying the corresponding treatment days by the deterioration acceleration rate calculated in the step (B).

  The relationship line for selecting an arbitrary point for determining the life index is the “relationship between the number of treatment days in the deterioration promoting treatment and the oxidation start temperature of the polyolefin material” created in the step (A), and “deterioration” described later. The relationship between the number of treatment days in the acceleration treatment and the remaining ratio of the antioxidant contained in the polyolefin material ”is created.

In the present invention, after passing through the step (B), the sample subjected to the deterioration accelerating treatment is freeze-pulverized, a predetermined amount of the pulverized material is extracted with chloroform, and the resulting chloroform extract is subjected to gas chromatography mass spectrometry (GC / MS: Gas Chromatography / Mass Spectrometry (HPLC) and High Performance Liquid Chromatography (HPLC) quantitate the antioxidant contained in the sample, and calculate the residual ratio of the antioxidant in the sample from this quantified value. .
Then, using the obtained remaining rate, a relationship between the remaining rate of the antioxidant and the number of processing days of the deterioration promoting process is obtained. Specifically, a relationship line (for example, a graph shown in FIG. 2) is created in which one axis (for example, the horizontal axis) is the number of processing days and the other axis (for example, the vertical axis) is the remaining ratio of the antioxidant.

  And as described above, "Relationship between the number of treatment days in the deterioration promotion treatment and the oxidation start temperature of the polyolefin material" and "Relationship between the treatment days in the deterioration promotion treatment and the remaining ratio of the antioxidant contained in the polyolefin material" And the relationship between the oxidation start temperature of the polyolefin material and the residual ratio of the antioxidant contained in the polyolefin material. Specifically, a relationship line (for example, a graph shown in FIG. 5) is created in which one axis (for example, the horizontal axis) is the remaining ratio of the antioxidant and the other axis (for example, the vertical axis) is the oxidation start temperature.

The relationship line created here shows a behavior in which the oxidation start temperature also decreases as the antioxidant decreases, and the oxidation start temperature changes abruptly when the antioxidant decreases to a certain amount. Specifically, for example, as the amount of antioxidant decreases, the oxidation start temperature decreases linearly at a slope A, and when the amount of antioxidant reaches a certain amount, a straight line at a larger slope B (B> A). In particular, a relational line in which the oxidation start temperature decreases appears. That is, this relationship line has two relationship lines (for example, the time when the oxidation start temperature rapidly decreases, that is, the time when deterioration starts to progress rapidly (for example, the bending point in FIG. 5 (treatment days: 52 days)). It is represented by a bent line having a bending point such that the lines (1) and (2) in FIG. 5 intersect.
This inflection point is considered to appear because the molecular structure of the polyolefin material changes greatly, and this inflection point can be regarded as a point indicating the life of the polyolefin material.

  In addition, any point (including the bending point) existing on the relationship line between the oxidation start temperature of the polyolefin material and the remaining ratio of the antioxidant contained in the polyolefin material is an index for determining the life of the polyolefin material. Can be used. In particular, the inflection point is a point indicating a lifetime assuming danger avoidance such as breakage or collapse of the polyolefin material. For example, the remaining ratio of the antioxidant is higher than the inflection point, that is, the treatment days are short (for example, in FIG. 5). The plot on the line (1) or a point (not shown) can be regarded as a point indicating the life of the safe side because the deterioration is smaller than the inflection point.

Then, an arbitrary point on the relation line (including the bending point) is determined as an index of the lifetime of the polyolefin material. For example, the process (B) is performed on the processing days corresponding to the arbitrary point on the line (1) in FIG. The lifetime of the polyolefin material is calculated by multiplying the deterioration acceleration rate calculated in (1). The number of processing days corresponding to an arbitrary point can be obtained from FIG. 2 or FIG.
(Processing days corresponding to any point) x (Deterioration promotion rate) = Life of polyolefin material

Examples of the polyolefin in the present invention include polyethylene, polypropylene, polybutadiene and the like. Among these, polypropylene is preferable because it is prone to oxidative degradation and has a great advantage of estimating the life.
Examples of polypropylene include a propylene homopolymer, a propylene-α-olefin random copolymer, a propylene-α-olefin block copolymer, and the like.

<Manufacturing method of polyolefin pipe>
The method for producing a polyolefin tube of the present invention includes a step of selecting a polyolefin material having a life estimated by the life estimation method of the present invention described above that is a predetermined reference value or more (hereinafter referred to as a “polyolefin material selection step”). And a step of manufacturing a polyolefin pipe using the selected polyolefin material (hereinafter referred to as “polyolefin pipe manufacturing step”).

-Polyolefin material selection process-
In the polyolefin material selection process, the polyolefin material used under the desired environmental conditions is estimated by the lifetime estimation method of the present invention described above, and a polyolefin material whose estimated lifetime is a predetermined reference value or more is selected. To do. Thereby, the characteristic requested | required of a raw material in manufacturing a polyolefin pipe | tube is securable.

  In this step, the life of the polyolefin material itself, which is a raw material used for pipe production, or a polyolefin pipe produced therefrom is estimated, and whether the estimated life is a value equal to or greater than a predetermined reference value (for example, a life of 20 years). The polyolefin material is selected based on whether or not. Here, when the estimated lifetime is less than the reference value, the polyolefin material is excluded, and a polyolefin material that can be used in the polyolefin tube manufacturing process described later is selected.

  This step may be performed on all polyolefin materials used as raw materials, or the polyolefin materials used as raw materials are arbitrarily sampled at a predetermined timing, and are performed only on arbitrarily selected polyolefin materials. It may be.

-Polyolefin tube manufacturing process-
In the polyolefin pipe manufacturing process, a polyolefin pipe is manufactured using the polyolefin material selected in the polyolefin material selection process. Thereby, it is possible to stably manufacture a polyolefin tube having a desired life.
There is no restriction | limiting in particular about the method of manufacturing a polyolefin pipe | tube, The conventionally well-known method of manufacturing a pipe | tube using polyolefin material can be selected suitably.
In addition, the shape of the manufactured polyolefin pipe, such as the size and the wall thickness of the pipe, is not particularly limited.

  The polyolefin material and the polyolefin pipe in the present invention are, for example, water circulation pipes used in apparatuses installed outdoors such as solar heat collecting panels (for example, water heated inside the pipe (preferably hot water of 60 ° C. to 80 ° C. ) Is suitably used for hot water piping).

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof. In the following examples, the hot water polypropylene pipe is also simply referred to as “polypropylene pipe”.

Example 1
−Preparation of co-samples−
For the joint specimen, a new warm water polypropylene pipe (hereinafter referred to as “unused product”) that is not actually used is prepared as an unused member, and the hot water that is actually used outdoors as a used member. A polypropylene tube for use (hereinafter referred to as “used product”) was prepared. As the above-mentioned used products, two polypropylene tubes used as hot water distribution pipes in which unused products were installed outdoors for 443 days and 734 days and hot water (about 60 ° C.) circulated were used.

  The unused and used polypropylene pipes used for the co-samples are formed from a polypropylene tube having the number average molecular weight and the degree of oxidative degradation shown in Table 1 below. The measured tensile strength. Further, in general, an antioxidant is contained in a polypropylene tube to prevent oxidation, and an example of the antioxidant contained in the sample is shown in Table 2 below.

In the above, the tensile strength, number average molecular weight, and oxidative deterioration degree were determined by the following methods.
(1) Tensile strength The specimen was cut into a ring shape with an axial length of 2 mm, and a tensile test was performed at a tensile speed of 100 mm / min using a tensile tester (Autograph AG-I 5 kN / manufactured by Shimadzu Corporation). . As shown in FIG. 7, the extension direction when the ring-shaped co-test body is pulled is the ring diameter direction.
(2) Number average molecular weight Using a high temperature GPC (Gel Permeation Chromatography) (HLC-8121GPC / HT / manufactured by Tosoh Corporation), the number average molecular weight of the specimen was measured. The high temperature GPC was measured under the conditions shown in Table 3 below.
(3) by oxidation deterioration degree reflection infrared spectrometer (FT-IR), the absorption by C-H in the vicinity of wave number 1720 cm ^-1 or 1730 cm ^-1 vicinity of a carbonyl group derived from the contemplated absorption and 1460 cm ^-1 The intensity ratio (I ₁₇₃₀ / I ₁₄₆₀ or I ₁₇₂₀ / I ₁₄₆₀ ) was calculated and used as the degree of oxidation degradation.

−Preparation of deterioration promoting samples−
The outer surface of an unused polypropylene tube was subjected to tube deterioration promotion treatment under the following conditions. Specifically, the outer surface of the polypropylene tube was irradiated with light continuously with a xenon lamp, and water was sprayed for 18 minutes in 120 minutes to wet the outer surface. Such a deterioration promotion process was repeated for 100 days to prepare a deterioration promotion sample. Various analysis samples were collected from the surface irradiated with light and analyzed.
<Condition>
Equipment used: accelerated weathering tester (Super Xenon Weather Meter SX2D-75 (manufactured by Suga Test Instruments Co., Ltd.), light source: xenon arc lamp (120 ± 5 W / m ² ))
・ Irradiation panel temperature: 63 ± 2 ℃
-Irradiation time: Continuous irradiation-Wetting method: Spraying water at about 20 ° C-Wetting cycle: Wetting time (spraying time) 18 minutes / 120 minutes, Drying time 102 minutes / 120 minutes

-Lifetime estimation-
About the deterioration acceleration | stimulation sample obtained above, the change (residual rate) of antioxidant with time was calculated | required with the following method.
-Antioxidant residual rate-
Chloroform extraction was performed on the deterioration-accelerated sample that had been frozen and ground, and the resulting chloroform extract was analyzed by gas chromatography mass spectrometry (GC / MS) and high performance liquid chromatography (HPLC). The antioxidant contained in the deterioration promoting sample was quantified. From the obtained quantitative value, the residual ratio of the antioxidant in the deterioration promoting sample was calculated. The measurement conditions of GC / MS and HPLC are shown in Table 3 and Table 4, respectively.

Next, FIG. 2 shows the relationship between the remaining ratio of the antioxidant and the number of processing days for the deterioration promoting process in the deterioration promoting sample subjected to the deterioration promoting process.
As shown in FIG. 2, as the number of treatment days elapses, the remaining amount of the antioxidant in the deterioration-promoting sample decreases, and when the number of treatment days exceeds 50 days, the decrease in the remaining rate becomes gradual. It is conceivable that the oxidation deterioration was suppressed by consumption of the acid value antioxidant, but after a predetermined proportion of the antioxidant was consumed, a peroxide that accelerates the progress of deterioration was significantly generated. It is inferred that the number average molecular weight is significantly reduced. A significant decrease in the number average molecular weight is considered to mean that the molecular structure of the deterioration promoting sample has collapsed. Therefore, in evaluating the life of the specimen, it is important to evaluate with an index that can predict the decrease in the number average molecular weight, that is, the onset of oxidative degradation.

  FIG. 3 shows the relationship between the number average molecular weight (Mn) and the antioxidant residual ratio. As shown in FIG. 3, it can be seen that the molecular weight of the deterioration promoting sample is lowered even in the state where the antioxidant remains. That is, it is suggested that even before the antioxidant is completely consumed, there is a possibility that the molecular structure collapses due to the progress of the molecular chain scission. Then, in the life evaluation using the antioxidant remaining ratio as an index, there is a possibility that an estimation result on the dangerous side is obtained.

  Therefore, with respect to the deterioration accelerating sample containing an antioxidant as an additive, the reduction of the number average molecular weight of the deterioration accelerating sample, that is, the start of oxidative deterioration was examined using the oxidation start temperature as an index. The oxidation start temperature was determined by the following method.

-Oxidation start temperature-
1 mg of a sample piece is collected from the freeze-pulverized deterioration promoting sample, and the sample is elevated in an oxygen atmosphere by using a differential scanning calorimeter (DSC: Differential Scanning Calorimeter, STAR System DSC-30, manufactured by METTLER TOLEDO). The oxidation start temperature (° C.) was determined at a temperature rate of 10 ° C./min. This oxidation start temperature is a temperature indicating the starting point of the increase in heat quantity of the exothermic peak that appears due to oxidation when the temperature of the sample piece is raised at a predetermined rate.

FIG. 4 shows the change over time in the oxidation start temperature of the sample with accelerated deterioration.
As shown in FIG. 4, it can be seen that the oxidation start temperature decreases as the number of treatment days in the deterioration promoting sample elapses. And after 70 days passed, the oxidation start temperature decreased remarkably.

FIG. 5 shows the relationship between the oxidation start temperature and the antioxidant remaining rate obtained from FIGS.
As shown in FIG. 5, a rapid change was observed at the point where the oxidation start temperature reached 236 ° C. (bending point; number of treatment days: 52 days). Therefore, the relationship between the oxidation start temperature and the remaining ratio of the antioxidant can be approximated by two lines bent at this point. That is, this suggests that a large change has started in the molecular structure in the deterioration promoting sample after the 52 days of treatment, and can be inferred as a sign of collapse of the molecular structure.
As described above, the significant decrease in the number average molecular weight of the polypropylene tube can be captured using the oxidation start temperature as an index.

Next, each of the used product A (443 days) and the used product B (734 days) was used, and each oxidation start temperature (° C.) was measured in the same manner as described above. The measurement results are as follows.
Oxidation start temperature of product A: 269 ° C
Oxidation start temperature of product B: 266 ° C

The oxidation start temperatures of the used products A and B were applied to FIG. The details are shown in FIG. As shown in FIG. 6, the processing days of the used products A and B were 2.5 days and 3.8 days, respectively.
Then, as described below, the deterioration promotion rate was calculated by dividing the number of days of use of the used products A and B (443 days and 734 days) by the number of days of processing of the used products A and B obtained above.
Deterioration acceleration rate of product A = 443 / 2.5 = 177.2
Deterioration promotion rate of used product B = 734 / 3.8 = 193.2

Next, in the relationship line between the oxidation start temperature and the antioxidant remaining rate indicated by two lines intersecting at the bending point as shown in FIG. 5, the bending point (treatment days: 52 days) is defined as an index of life, The lifetime of the used products A and B was calculated by multiplying the number of treatment days (52 days) by the deterioration acceleration rate. In addition, as shown in FIG. 5, it was confirmed that both used goods A and B exist on the line (1).
Life of product A: (52 days × 177.2) / 365 days = 25.2 years Life of product B: (52 days × 193.2) / 365 days = 27.5 years

  In the present embodiment, the case where the inflection point (the number of treatment days: 52 days) is defined as the life index and the life is estimated has been shown. However, the present invention is not limited to this. It is also possible to select an arbitrary point and define it as a life index, and to estimate the life on the safe side in the same manner as described above.

In the present embodiment, as described above, when the lifetimes of the used products A and B are estimated to be 25.2 years and 27.5 years, and this is equal to or greater than a predetermined reference value serving as a lifetime threshold, The polypropylene forming B can be selected as a suitable material that is expected to have a desired life when a polypropylene tube is manufactured. For example, when the standard value (lifetime) for determining the life is 20 years, the products A and B both exceed the standard value, and the polypropylene forming the products A and B is It is selected as a material that develops the expected life. Then, by producing a propylene pipe using the selected polypropylene, a polypropylene pipe having a predetermined life (here, 20 years or more) is stably produced.
A polypropylene tube can be produced by appropriately selecting a conventionally known method.

Claims (7)

A method for estimating the lifetime of a polyolefin material containing an antioxidant,
The oxidation start temperature of the polyolefin material forming the used member is measured, and the obtained measurement value is calculated as the number of treatment days in the deterioration promotion treatment performed on the polyolefin material forming the unused member and the oxidation start temperature of the polyolefin material. Applying the above relationship to find the corresponding processing days,
Dividing the use days of the use member by the corresponding processing days to calculate a deterioration promotion rate by the deterioration promotion process;
A polyolefin prepared based on the relationship between the number of treatment days in the deterioration accelerating treatment and the oxidation start temperature of the polyolefin material, and the relationship between the number of treatment days in the degradation accelerating treatment and the residual ratio of the antioxidant contained in the polyolefin material. An arbitrary point on the relationship line between the oxidation start temperature of the material and the remaining ratio of the antioxidant contained in the polyolefin material is defined as an index of the lifetime of the polyolefin material, and the deterioration acceleration rate is determined in the treatment days corresponding to the arbitrary point. To calculate the lifetime of the polyolefin material,
Only including,
The deterioration promoting process is a method for estimating the lifetime of a polyolefin material, which is at least one of a process of performing heat treatment and water contact, and a process of performing light irradiation and water contact .   The life estimation method according to claim 1, wherein the arbitrary point is a bending point on the relation line.   The lifetime estimation method according to claim 1, wherein the polyolefin material is a polypropylene material.   The life estimation method according to any one of claims 1 to 3, wherein the used member and the unused member are water circulation pipes through which heated water flows.   The lifetime estimation method according to any one of claims 1 to 4, wherein the oxidation start temperature is measured by differential scanning calorimetry.   The life estimation method according to any one of claims 1 to 5, wherein the deterioration promoting process is a process of performing light irradiation and water spray using a xenon lamp as a light source on a polyolefin material. A step of selecting a polyolefin material having a lifetime estimated by the lifetime estimation method according to any one of claims 1 to 6 being a predetermined reference value or more;
Producing a polyolefin pipe using the selected polyolefin material;
A method for producing a polyolefin tube comprising: