Patent Description:
Since plumbing pipes used in heating pipes are constructed inside buildings, they should have excellent long-term durability so as to prevent water leakage due to cracks. Known methods for evaluating long-term durability of plumbing pipes are ISO <NUM> and ISO <NUM>, and the like. ISO <NUM> is a method of estimating the pressure expected to cause cracks over <NUM> years by measuring the crack occurrence time over one year according to the temperature and pressure of water passing through a pipe and extrapolating this. Products with long-term durability recognized by ISO <NUM> have environmental stress crack resistance (ESCR) of about <NUM>,<NUM> hours or more, as measured at a stress of <NUM> MPa and a temperature of <NUM> by full notch creep test (FNCT) according to ISO <NUM>. That is, according to the above method, the relevant product has durability to the extent that the sample breaks after <NUM>,<NUM> hours or more must elapse. However, there is a problem that it takes at least <NUM> months to <NUM> year or more to perform the two methods. Therefore, a method capable of predicting long-term durability in a quick way is required, so that product development time can be shortened by selecting a sample to be measured for long-term durability among various samples in the product development stage.

Furthermore, it is considered that the long-term durability of the pipe used in the above application is affected by the characteristics of the resin used for forming the pipe. Therefore, there is a need for a polymer-related design standard that can ensure long-term durability of the pipe.

It is one object of the present application to provide a method for predicting long-term durability of a resin composition for piping in a short time.

It is another object of the present application to provide a method for comparatively evaluating long-term durability for a plurality of resin compositions for piping.

It is another object to provide a polymer (not according to the invention) which can be used for manufacturing a heater-plumbing pipe having excellent long-term durability.

It is another object to provide a resin composition (not according to the invention) for heater-piping having excellent environmental stress crack resistance.

The above objects and other objects of the present application can be all solved by the present application which is described in detail below.

The present invention is set out in the appended set of claims and relates to a method for predicting or evaluating long-term durability of a resin composition for piping.

In the present application, the sample to be predicted or evaluated may be a resin or a resin composition containing other components. Furthermore, in the present application, the resin (composition) for piping may mean a resin (composition) used in a pipe forming a moving path of a fluid, and may mainly mean a resin (composition) for heater-piping.

The long-term durability prediction method of the present application as set out in the appended set of claims uses a tie molecule, an entanglement molecular weight (Me) and a mass-average molecular weight (Mw) as factors for predicting long-term durability.

In the present application, the tie molecule, which is one of the factors used for predicting long-term durability, means a polymer molecule connecting crystals of an amorphous polymer resin. In the amorphous polymer molecule, crystals of lamellar structures are formed by chain folding below a crystallization temperature. At this time, if a polymer structure capable of forming a defect in the crystal structure, for example, an α-olefin or an LCB (long chain branch), is present, the relevant moiety does not form crystals and remains amorphous. On the other hand, the lamellar structures can be formed in the moiety where no α-olefin or LCB structure is present, so that one polymer chain can form crystalline-amorphous-crystalline structures. In such a structure, the amorphous moiety serves to connect the crystal to the crystal, which is referred to as a tie molecule. As the polymer molecule has a high molecular weight and thus the length of the polymer chain is longer, the probability that the tie molecules will be produced increases. As described above, the higher the content of the tie molecules is, the stronger the connection between the crystal structures is, and thus it is considered that crack generation and propagation become difficult. Taking this point into consideration, in the present application, the content of tie molecules is used as one factor for predicting long-term durability. At this time, the content of tie molecules means a % ratio, that is, a wt%, of the polymer molecules forming the tie molecules based on the weight <NUM> of the entire polymer molecule contained in the resin composition. The content of tie molecules can be determined as described below.

When one polymer chain is tangled with the surrounding polymers or itself to form an entanglement point functioning as a physical crosslink, the entanglement molecular weight (Me), which is another factor used in the present application method, means an average molecular weight between such entanglement points. As the polymer molecule has a high molecular weight and thus the length of the polymer chain is longer, the probability that entanglement points will be generated increases, so that the entanglement molecular weight decreases. The smaller the entanglement molecular weight, the greater the entanglement degree of the polymer, and thus it is considered that the resistance to external force increases. Taking this point into consideration, in the present application, the entanglement molecular weight is used as one of factors of long-term durability prediction. The entanglement molecular weight can be measured as described below.

Another of the factors used in the long-term durability prediction of the present application is the content of an ultrahigh molecular weight component. At this time, the ultrahigh molecular weight means a case where the mass average molecular weight (Mw) is <NUM>,<NUM>,<NUM> or more, and the content of the ultrahigh molecular weight component means a % ratio, that is, a wt%, of the polymer having a mass average molecular weight of <NUM>,<NUM>,<NUM> or more based on the weight <NUM> of the entire polymer contained in the resin composition. The higher the content of the ultrahigh molecular weight component, the larger the number of polymer molecules having a longer polymer chain length, and thus it is considered that the entanglement of the polymer chain or the content of tie molecules increases. Taking this point into consideration, in the present application, the content of the ultrahigh molecular weight component is used as one factor for predicting the long-term durability. The content of the ultrahigh molecular weight component can be measured as described below.

According to the present application in which the above factors are used for the long-term durability measurement of a resin composition as a sample, the long-term durability of the resin composition can be predicted or evaluated in a short time even if a small amount of a sample is used.

Specifically, the method according to the present application predicts or evaluates the long-term durability of a resin composition as a sample by using the following equation.

In Equation above, a=<NUM>,<NUM>, b=<NUM>, c=-<NUM>, and d=<NUM>. Furthermore, X, Y and Z are values relating to molecular characteristics measured in a resin composition as a sample, respectively. Specifically, X means a content (wt%) of tie molecules, Y means an entanglement molecular weight (g/mol), and Z means a content (wt%) of a component having a mass average molecular weight (Mw) of <NUM>,<NUM>,<NUM> or more. At this time, X, Y and Z are used as dimensionless constants excluding the units.

The inventors of the present application have confirmed that the predicted value concerning the long-term durability calculated according to Equation above is very similar to the environmental stress crack resistance evaluation result actually measured by the full notch creep test (FNCT) according to ISO <NUM> at <NUM> MPa and <NUM>. Therefore, if a predicted value of the long-term durability of a resin composition as a sample is calculated according to the present application, the long-term durability of a resin composition for piping can be predicted or evaluated in a short time by only simple calculation without performing the durability evaluation over a long period of time such as ISO <NUM> or ISO <NUM>.

In the present application, the predicted value calculation of long-term durability can be made for a plurality of samples. In this case, it can be determined that the long-term durability of the sample having the largest calculated value is the most excellent.

In the present application, a sample to be predicted or evaluated for long-term durability, that is, a resin composition may comprise a homopolymer formed from one monomer component and/or a copolymer formed from a plurality of different monomer components. Then, the resin composition may also comprise one or more homopolymers or copolymers.

In one example, the resin composition as the sample may comprise a polyolefin. The kind of the polyolefin is not particularly limited. For example, the polyolefin may be a polymer formed from ethylene, butylene, propylene, and/or α-olefinic monomers. The kind of the α-olefinic monomer is not particularly limited. For example, <NUM>-butene, <NUM>-pentene, <NUM>-methyl-<NUM>-pentene, <NUM>-hexene, <NUM>-heptene, <NUM>-octene, <NUM>-decene, <NUM>-undecene, <NUM>-dodecene, <NUM>-tetradecene, <NUM>-hexadecene, <NUM>-octadecene or <NUM>-eicosene can be used, without being particularly limited thereto.

In one example, the present application relates to an olefinic polymer (not according to the invention). The polymer can be used in a pipe forming a moving path of a fluid, and can be mainly used for forming a heating pipe. Since the polymer satisfies predetermined conditions and/or configurations to be described below, it has excellent long-term durability which can be confirmed, for example, through evaluation of environmental stress crack resistance.

As design factors of the olefinic polymer, a content of tie molecules, an entanglement molecular weight (Me) and a content of an ultrahigh molecular weight component can be used.

The tie molecule, which is one of the design factors of a polymer, means a polymer molecule connecting crystals of an amorphous polymer resin. In the amorphous polymer molecule, crystals of lamellar structures are formed by chain folding below a crystallization temperature. At this time, if a polymer structure capable of forming a defect in the crystal structure, for example, an α-olefin or an LCB (long chain branch), is present, the relevant moiety does not form crystals and remains amorphous. On the other hand, the lamellar structures can be formed in the moiety where no α-olefin or LCB structure is present, so that one polymer chain can form crystalline-amorphous-crystalline structures. In such a structure, the amorphous moiety serves to connect the crystal to the crystal, which is referred to as a tie molecule. As the polymer molecule has a high molecular weight and thus the length of the polymer chain is longer, the probability that the tie molecules will be produced increases. As described above, the higher the content of the tie molecules is, the stronger the connection between the crystal structures is, and thus it is considered that crack generation and propagation become difficult. Taking this into consideration, the content of tie molecules is used as one factor of the polymer design. At this time, the content of tie molecules means a % ratio, that is, a wt%, of the (polymer) component forming the tie molecules based on the weight <NUM> of the entire polymer molecule contained in the resin composition. The content of tie molecules can be determined as described below.

When one polymer chain is tangled with the surrounding polymers or itself to form an entanglement point functioning as a physical crosslink, the entanglement molecular weight (Me), means an average molecular weight between such entanglement points. As the polymer molecule has a high molecular weight and thus the length of the polymer chain is longer, the probability that entanglement points will be generated increases, so that the entanglement molecular weight decreases. The smaller the entanglement molecular weight, the greater the entanglement degree of the polymer, and thus it is considered that the resistance to external force increases. Taking this point into consideration, the entanglement molecular weight is used as one factor in the polymer design. The entanglement molecular weight can be measured as described below.

Another of the factors used is the content of an ultrahigh molecular weight component. At this time, the ultrahigh molecular weight means a case where the mass average molecular weight (Mw) is <NUM>,<NUM>,<NUM> or more, and the content of the ultrahigh molecular weight component means a % ratio, that is, a wt%, of the (polymer) component having a mass average molecular weight of <NUM>,<NUM>,<NUM> or more based on the weight <NUM> of the entire polymer. The higher the content of the ultrahigh molecular weight component, the larger the number of polymer molecules having a longer polymer chain length, and thus it is considered that the entanglement of the polymer chain or the content of tie molecules increases. Taking this point into consideration, the content of the ultrahigh molecular weight component is used as one factor of the polymer design. The content of the ultrahigh molecular weight component can be measured as described below.

The inventors of the present application have confirmed that when the olefinic polymer (not according to the invention) is designed to satisfy a predetermined relationship with regard to such factors, it is possible to provide a resin for heater-piping having excellent long-term durability. Specifically, the olefinic polymer may be an olefinic polymer satisfying at least two conditions of the following conditions [A] to [C].

When at least two conditions of [A] to [C] are satisfied, it is possible to show excellent long-term durability characteristics in the environmental stress crack resistance (ESCR) evaluation measured by the full notch creep test (FNCT) according to ISO <NUM> at <NUM> MPa and <NUM>. For example, time characteristics to be described below can be satisfied.

In one example, the polymer may further satisfy the condition that the content of tie molecules is <NUM> wt% or less, <NUM> wt% or less, or <NUM> wt% or less with regard to the above condition [A]. Upon designing the polymer for the predetermined application, in consideration of the significance that the content of tie molecules as described above has, an increase in the content can be considered. To increase the content of tie molecules, the density of the polymer should be lowered or the content of the higher molecular weight component should be increased. However, if the density decreases, the pressure-resistant performance of the final pipe product declines, and if the content of the polymer component increases, the viscosity increases, whereby there is a problem that the processability deteriorates, so that it is preferable to control the content of tie molecules in the above content range.

In another example, the polymer may further satisfy the condition that the entanglement molecular weight (Me) is <NUM>/mol or more, <NUM>/mol or more, <NUM>/mol or more, <NUM>/mol or more, or <NUM>/mol or more with regard to the above condition [B]. Upon designing the polymer for the predetermined application, in consideration of the significance that the content of the entanglement molecular weight as described above has, a decrease in the molecular weight can be considered. However, when the entanglement molecular weight is too low, the content of the high molecular weight component becomes high, so that the processability is lowered. In addition, since breakage easily occurs in the stretching process for adjusting dimensions, such as a diameter or a thickness after extruding the produced pipe, there is also a need to stretch it at a low speed, so that there is a problem that productivity is lowered. Therefore, it is preferable to have a molecular weight within the above range.

In another example, the polymer may further satisfy the condition that the content of the component having a mass average molecular weight (Mw) of <NUM>,<NUM>,<NUM> or more is <NUM> wt% or less, <NUM> wt% or less, or <NUM> wt% or less with regard to the above condition [C]. If the content of the ultrahigh molecular weight component exceeds the above range, the processability may be deteriorated.

In another example, the polymer may satisfy all of the conditions [A] to [C]. When all the three conditions are satisfied, more excellent long-term durability can be ensured.

The kind of the monomer for forming the olefinic polymer is not particularly limited. For example, the olefinic polymer may be formed from a monomer mixture comprising ethylene, butylene, propylene, or α-olefinic monomers. That is, the polymer may be one prepared by polymerizing one or more monomers of the above monomers. At this time, the kind of the α-olefinic monomer is not particularly limited. For example, <NUM>-butene, <NUM>-pentene, <NUM>-methyl-<NUM>-pentene, <NUM>-hexene, <NUM>-heptene, <NUM>-octene, <NUM>-decene, <NUM>-undecene, <NUM>-dodecene, <NUM>-tetradecene, <NUM>-hexadecene, <NUM>-octadecene or <NUM>-eicosene can be used, without being particularly limited thereto.

In one example, the monomer mixture may comprise two or more monomers selected from ethylene, butylene, propylene, and α-olefinic monomers. At this time, the two or more monomers contained in the monomer mixture may be different from each other, where the kind of the α-olefinic monomer is the same as those listed above.

In one example, the olefinic polymer may comprise ethylene as a main component. In relation to the components of the polymer, the main component monomer may means a case where the content of the main component monomer exceeds <NUM> wt% based on the content <NUM> of the total monomers used for forming the polymer. The upper limit of the main component monomer content is not particularly limited, but may be, for example, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, <NUM> wt% or less, or <NUM> wt% or less. In this case, the monomer mixture may comprise one or more monomers selected from butylene, propylene, and α-olefinic monomers as a copolymerizable monomer, in addition to ethylene as the main component. The copolymerizable monomer may be used in the monomer mixture as much as the remaining content other than the content of ethylene as the main monomer.

In one example, <NUM>-butene (<NUM>-C4) may be used as the copolymerizing monomer for forming the olefinic polymer. Specifically, a monomer having a short length, for example, <NUM>-butene may be used due to influences of the characteristics of the polymerization equipment or the supply and demand of raw materials. However, in such a case, the long-term durability may be lowered as compared with a product produced using a relatively long copolymerizing monomer, for example, <NUM>-hexene (<NUM>-C6) or <NUM>-octene (<NUM>-C8). However, when the above-described conditions are satisfied, superior long-term durability can be ensured even when a copolymerizing monomer having a relatively short length such as <NUM>-butene is used. The content of <NUM>-butene to be used is not particularly limited, but may be used so as to satisfy a range of <NUM> to <NUM>/<NUM>,000C as a result of FT-IR analysis.

The polymer satisfying the above conditions and configuration may have environmental stress cracking resistance (ESCR) of <NUM> hours or more measured by the full notch creep test (FNCT) according to ISO <NUM> at <NUM> MPa and <NUM>. More preferably, the polymer may have environmental stress cracking resistance (ESCR) of <NUM> hours to <NUM> hours measured by the full notch creep test (FNCT) according to the same conditions and method.

According to one example of the present application, a method capable of predicting long-term durability of a resin for piping in a short time using a small amount of a sample can be provided. Also, according to the present application, since the long-term durability of the resin for piping can be evaluated in a short time, a polymer structure having excellent long-term durability can be usefully designed and a sample that is worth actually measuring long-term durability can be selected in a short time, so that the efficiency of the product development stage can be improved and the development time can be shortened. In addition, an olefinic polymer structure (not according to the invention) having excellent long-term durability can be usefully designed, and a plumbing pipe having excellent long-term durability can be provided.

<FIG> is a graph showing the correlation between FNCT measured values of the resin used in a Preparation Example and FNCT predicted values calculated for each resin of the present application examples corresponding to the Preparation Example.

Hereinafter, the present application will be described in detail through examples. However, the present invention is not limited by the following examples but as set out in the appended set of claims.

The relevant physical properties measured in the following experimental examples were measured according to the following methods.

In Equation <NUM> above, r is an end-to-end distance of a random coil, b<NUM> is <NUM>/2r<NUM>, lc is a crystal thickness, which is obtained from Equation <NUM> below, and la is an amorphous thickness, which is obtained from Equation <NUM> below.

In Equation <NUM> above, T°m is <NUM>, σe is <NUM> x <NUM>-<NUM> J/m<NUM>, and Δhm is <NUM> x <NUM><NUM> J/m<NUM>.

In Equation <NUM> above, ρc is a crystal density, which is <NUM>,<NUM>/m<NUM>, ρa is a density of amorphous phase, which is <NUM>/m<NUM>, ωc is weight fraction crystallinity, which is confirmed from DSC results.

However, in Equation above, a=<NUM>,<NUM>, b=<NUM>, c=-<NUM>, and d=<NUM>, X, Y and Z mean, in a resin composition as a sample, a content (wt%) of tie molecules, an entanglement molecular weight (g/mol) and a content (wt%) of a component having a mass average molecular weight (Mw) of <NUM>,<NUM>,<NUM> or more, respectively. At this time, in Equation above, X, Y and Z are used as dimensionless constants excluding the units.

Based on the predicted value calculated from Equation above, the characteristics of the resin were classified qualitatively by the following criteria.

A resin as a target for long-term durability measurement was prepared as follows. Then, the time was measured according to the FNCT (full notch creep test). The results are shown in Table <NUM>.

Preparation Example <NUM>: In a hexane slurry CSTR process, the resin was polymerized while supplying ethylene, hydrogen and <NUM>-butene at a predetermined input rate using a metallocene catalyst. The prepared resin had a density of <NUM>/cm<NUM> as measured according to ASTM D <NUM> and an MI (melt index) of <NUM> as measured under conditions of <NUM> and <NUM>/<NUM> according to ASTM D <NUM>.

Preparation Example <NUM>: A resin was prepared in the same manner as in Preparation Example <NUM>, except that the input rate of the raw materials was controlled differently. The density of the prepared resin was <NUM>/cm<NUM> and the MI was <NUM>.

Preparation Example <NUM>: A resin was prepared in the same manner as in Preparation Example <NUM>, except that the density was <NUM>/cm<NUM> and the MI measured under the same conditions was <NUM>.

Preparation Example <NUM>: A resin was prepared in the same manner as in Preparation Example <NUM> except that the density was <NUM>/cm<NUM> and the MI measured under the same conditions was <NUM>.

For the sample prepared in Preparation Example <NUM>, the content of tie molecules, the entanglement molecular weight, and the content of the ultrahigh molecular weight component were measured according to the above methods, and the predicted value concerning long-term durability was calculated by substituting them into Equation according to the present application. The result is as shown in Table <NUM>.

The contents of tie molecules, the entanglement molecular weights and the contents of the ultrahigh molecular weight components were measured and the predicted values concerning the durability were calculated, in the same manner as in Example <NUM>, except that in Examples <NUM> to <NUM>, the resins prepared in accordance with Preparation Examples <NUM> to <NUM> in this order were used, respectively.

Comparing the FNCT measured values in Table <NUM> with the dimensionless calculated values in Table <NUM>, it can be seen that their values are very similar. Then, it can be confirmed that the measured values and the calculated values can be evaluated very similarly even in the qualitative classification. Actually, it is also confirmed in <FIG> that the X-axis and the Y-axis have a strong linear correlation. That is, the durability prediction method of the present application can replace the conventional FNCT measurement method. In other words, the method according to the present application can evaluate the durability of the resin (composition) for piping in a short time without going through a testing period of several months or more.

The relevant physical properties measured for the polymers of Preparation Examples <NUM> to <NUM> (not according to the invention) were measured according to the methods described for Experimental Example <NUM>.

Preparation Example <NUM>: In a hexane slurry CSTR process, the resin was polymerized while supplying ethylene, hydrogen and <NUM>-butene at a predetermined input rate using a metallocene catalyst capable of producing a bimodal molecular weight distribution. The prepared resin had a density of <NUM>/cm<NUM> as measured according to ASTM D <NUM> and an MI (melt index) of <NUM> as measured under conditions of <NUM> and <NUM>/<NUM> according to ASTM D <NUM>.

Preparation Example <NUM>: A resin was prepared in the same manner as in Preparation Example <NUM>, except that a metallocene catalyst of a different kind from that of Preparation Example <NUM> was used. The density of the prepared resin was <NUM>/cm<NUM> and the MI was <NUM>.

For the sample prepared in each of Preparation Examples, the content of tie molecules, the entanglement molecular weight and the content of the ultrahigh molecular weight component were measured according to the above methods. Alternatively, for the sample prepared in each of Preparation Examples above, the environmental stress crack resistance measured by FNCT was measured. The results are as shown in Table <NUM>.

Claim 1:
A method for predicting long-term durability of a resin composition for piping,
wherein the method for predicting long-term durability of a resin composition for piping uses a content of tie molecules, an entanglement molecular weight (Me) and a mass average molecular weight (Mw) that the resin composition has, and
wherein the method for predicting long-term durability of a resin composition for piping uses Equation below: <MAT>
wherein, a=<NUM>,<NUM>, b=<NUM>, c=-<NUM>, and d=<NUM>, X, Y and Z mean, in the resin composition as a sample, a content (wt%) of tie molecules, an entanglement molecular weight (g/mol) and a content (wt%) of a component having a mass average molecular weight (Mw) of <NUM>,<NUM>,<NUM> or more, respectively, where X, Y and Z are used as dimensionless constants excluding the units, and
the content of tie molecules, the entanglement molecular weight (g/mol) and the content of a component having a mass average molecular weight (Mw) of <NUM>,<NUM>,<NUM> or more are obtained as described in the specification.