JPH0510900A - Estimation of heat history of polyethylene - Google Patents

Abstract

PURPOSE:To accurately and easily estimate the time of the heat history applied to polyethylene without being limited by temp. or a time. CONSTITUTION:The heat history temp. of polyethylene having received heat history is estimated and the fusion curve A due to a differential scanning calorimeter thereof is measured and the temp. of the low temp. peak appearing in the fusion curve A is calculated. The heat history temp. of polyethylene is estimated from the estimated heat history temp. and the temp. of a peak L on a low temp. side on the basis of a graph showing the relation between the heat history temp. and heat history time preliminarily calculated from polyethylene whose heat history is known and the peak tap. on the low temp. side.

Description

Detailed Description of the Invention

[Object of the Invention]

[0002]

FIELD OF THE INVENTION This invention relates to a method for estimating the thermal history time experienced by polyethylene using a differential scanning calorimeter.

[0003]

2. Description of the Related Art Polyethylene (crosslinked polyethylene, copolymers containing these polyethylenes, graft polymers,
Including blended rubber. same as below. ) Is widely used as an insulator for power cables and communication cables because it has excellent electrical insulation properties.

However, it is important for studying the improvement of the insulation performance of cable insulators to consider the thermal history of polyethylene during the manufacturing process and use of the cable and the accompanying change in crystal structure. Has meaning

As a method of estimating the heat history below the melting point of polyethylene, when polyethylene, which is a crystalline polymer, is subjected to a heat history within the melting temperature range, the rearrangement of crystal particles partially melted at that temperature occurs. Recrystallization on the basis of the melting point (hereinafter referred to as DSC curve) by a differential scanning calorimeter (hereinafter abbreviated as DSC) causes a new peak corresponding to the treatment temperature in addition to the main melting point peak. There is known a method of estimating a thermal history temperature by correcting a temperature showing this peak based on a new peak based on empirical data.

[0006] Further, after taking samples from polyethylene that has undergone thermal history below the melting point and polyethylene that has not undergone thermal history, a difference curve of the DSC curves of these samples is prepared.
Since the temperature showing the peak on the heat generation side of the difference curve hardly changes with the heat history time and substantially matches the heat history temperature, a method of estimating this as the heat history temperature is also known.

However, all of these methods estimate the heat history temperature, and cannot estimate the time when the heat history is received.

Recently, as a method of estimating the heat history time, a method of estimating the heat history time from the peak temperature on the heat generation side of the difference curve of the DSC curve and the temperature showing the peak on the heat absorption side has been devised.

However, according to this method, the heat history time can be estimated with relatively high accuracy up to a heat history temperature of about 90 ° C. However, if the heat history temperature exceeds 90 ° C. and the heat history time becomes long, the difference curve Since the endothermic peak temperature approaches the melting point and becomes unclear, there is a problem that it cannot be estimated or the accuracy decreases.

[0010]

As described above, according to the conventionally known method for estimating heat history of polyethylene, the heat history temperature can be estimated almost accurately, but the heat history time cannot be estimated by temperature or time. There were cases.

The present invention has been made in order to solve such a conventional problem, and the time of heat history received by polyethylene can be accurately and easily estimated without being limited by temperature or time. The purpose is to provide a method.

[Constitution of the Invention]

[0013]

SUMMARY OF THE INVENTION The present invention is a method for estimating the heat history time of polyethylene that has undergone a heat history below the melting point, while estimating the heat history temperature of polyethylene that has undergone this heat history. By measuring the melting curve of the polyethylene subjected to history with a differential scanning calorimeter, the temperature at which the melting curve shows the peak at the low temperature side of the two peaks at the lower temperature side than the melting point is obtained, and the estimated thermal history temperature The heat history time from the low-temperature side peak temperature, the heat history is obtained in advance with known polyethylene, it is estimated based on the measurement data showing the relationship between the heat history temperature and the heat history time and the low-temperature side peak temperature, To do. In the present invention, as a method for estimating the heat history temperature of polyethylene that has undergone heat history, there are known methods known in the art, such as a method of estimating based on the peak appearing in the DSC curve of polyethylene that has undergone heat history. It can be used, but above all,
From the point of accuracy, DSC of polyethylene subjected to heat history
The method of estimating by a difference curve between the curve and the DSC curve of the polyethylene sample which is not subjected to the heat history is preferable.

That is, according to this method, for example, the DSC curve A of polyethylene subjected to heat history as shown in FIG.
And the DSC curve B of a polyethylene sample that was not subjected to heat history
And a difference curve (A-B) is created, and the temperature at which the difference curve shows a peak (M) on the heat generation side at a temperature lower than the melting point is estimated as the heat history temperature.

As a method for preparing the difference curve, for example, (i) the DSC curves of the respective samples are separately measured by a known method, and the obtained curves are superposed by adjusting the temperature scales and the difference in the endothermic amount. (Ii) D of each sample
The SC curve was separately measured by a known method, and the obtained D
Subtract SC curve A to DSC curve B using a data processor. (Iii) Place a polyethylene sample that is not subject to heat history on the DSC standard sample side holder, and place a polyethylene sample that has been subjected to heat history on the measurement sample side holder. There is a method in which the difference curve is directly recorded by performing the DSC curve measurement by using the above method. In addition, as the sample that does not receive the thermal history used here, in addition to the sample that has not been subjected to the thermal history at all, the sample that has been subjected to the thermal history such as heating once is left to cool and the thermal history received is eliminated, Alternatively, a sample subjected to a thermal history may be used as a sample by further heating it to a temperature about 30 ° C. higher than its melting point and then rapidly cooling it to room temperature.

The reason why the temperature showing the peak (M) in the heat generation direction on the lower temperature side than the melting point in the difference curve obtained by such a method is estimated as the heat history temperature is as follows.

That is, when a crystalline polymer such as polyethylene is heated at a temperature equal to or lower than the melting point, the molecular chains forming fine crystals having a melting point at the heating temperature (heat history temperature) are melted at the main melting point. The number of microcrystals surrounded by the growth of the crystals and having a melting point at the heat history temperature when the temperature is returned to room temperature is smaller than that before the heat history is received, and as a result, the endothermic value at this temperature becomes small. This decrease in endotherm is due to DS
When a C-difference curve is created, it appears as a peak (M) on the heat generation side, so the temperature showing this peak (M) is estimated as the thermal history temperature. In addition, FIG. 2 shows the peak (M) temperature on the exothermic side (exothermic side peak temperature) of the DSC difference curve created for polyethylene with known thermal history temperature and thermal history time.
Is a graph showing the relationship between the actual heat history temperature and the heat history time.It is shown that the heat generation side peak temperature is almost the same as the heat history temperature actually received, and depending on the heat history time, It shows that it does not change.

In the present invention, the thermal history temperature is thus estimated and the D of the polyethylene subjected to the thermal history is estimated.
From the SC curve, the temperature at which the curve shows the peak on the low temperature side of the two peaks on the low temperature side of the melting point, eg, Fig. 1
In the example shown in, the two peaks (L) of DSC curve A
And (H), the temperature (low temperature side peak temperature) showing the low temperature side peak (L) is obtained, and from these estimated heat history temperature and low temperature side peak temperature, the heat history time of polyethylene that has undergone heat history To estimate.

That is, FIG. 3 is a graph showing the relationship between the peak temperature on the low temperature side of the DSC curve measured for polyethylene having a known heat history temperature and heat history time, and the actual heat history temperature and heat history time. As can be seen from this graph, the low-temperature side peak temperature depends on the heat history temperature and the heat history time, and decreases as the heat history time increases. The decrease in the temperature is almost proportional to the logarithm of the heat history time.

Therefore, a DSC curve is measured for polyethylene having a known heat history temperature and heat history time, the low temperature side peak temperature is read from this curve, and the heat history temperature and heat history time and the low temperature side peak temperature of the DSC curve are measured. The relationship of is expressed in a graph, table, or formula as shown in FIG. 3, for example, and the thermal history temperature estimated by the method described above for polyethylene with unknown thermal history and its DS
By fitting the low temperature side peak temperature obtained from the C curve as the heat history temperature and the low temperature side peak temperature, respectively, and calculating the relevant heat history time, this can be estimated as the heat history time of polyethylene whose heat history is unknown. ..

Since the low temperature side peak of the DSC curve clearly appears even when the thermal history temperature exceeds 90 ° C. or the time becomes long, the thermal history time can be widely estimated without being limited by the temperature and time. be able to.

[0022]

As described above, according to the method of the present invention, the estimated thermal history temperature and D
Since the heat history time is estimated from the low temperature side peak temperature of the SC curve, it is possible to accurately and easily estimate the heat history time received by polyethylene even when the heat history temperature exceeds 90 ° C or becomes long. You can

[0023]

EXAMPLES Examples of the present invention will be described below.

Example A DSC curve of a low density polyethylene (hereinafter referred to as LDPE) sample which was heat-treated under the conditions shown in Table 1 was measured, and the low temperature side peak temperature of each DSC curve was read. Further, a DSC difference curve between the heat-treated LDPE sample and the LDPE sample not subjected to the heat treatment was prepared, and the exothermic peak temperature of this DSC difference curve was read to estimate the heat history temperature.

Next, shown in FIG. 3, which is prepared in advance from the low temperature side peak temperature and the estimated thermal history temperature,
Each heat-treated LDPE is read by a graph showing the relationship between the heat history temperature and the heat history time, and the graph showing the relationship between the low temperature side peak temperature of the DSC curve measured with polyethylene having a known heat history temperature and heat history time. The thermal history temperature of the sample was estimated. The estimation result is shown in Table 1 together with the estimated thermal history temperature. (Margin) Table 1 Sample No. Actual heating temperature and time Estimated temperature and time according to the example 1 80 ℃ × 100 minutes 82 ℃ × 90 minutes 2 90 ℃ × 100 minutes 90 ℃ × 97 minutes 3 93 ℃ × 100 minutes 93 ℃ × 102 minutes 4 95 ℃ × 100 minutes 95 ℃ × 98 minutes 5 98 ℃ × 100 minutes 98 ℃ × 100 minutes 6 90 ℃ × 10 days 90 ℃ × 10 days 7 98 ℃ × 10 days 98 ℃ × 10 days

[0026]

As is apparent from the above examples, according to the method of the present invention, the peak temperature on the low temperature side of the DSC curve which can be clearly obtained even when the thermal history temperature exceeds 90 ° C. or the time becomes long. Since it is estimated based on the estimated thermal history temperature,
The heat history time received by polyethylene can be estimated widely, easily and almost accurately, without being limited by temperature and time.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the present invention and is a diagram showing an example of a DSC curve of polyethylene subjected to heat history, a DSC curve of polyethylene not subjected to heat history, and a difference curve between these curves.

FIG. 2 is a graph showing the relationship between heat history temperature and heat history time in polyethylene and the peak temperature on the heat generation side of the DSC difference curve.

FIG. 3 is a graph showing the relationship between heat history temperature and heat history time of polyethylene and the peak temperature on the low temperature side of the DSC curve.

Claims (1)

Claim: What is claimed is: 1. A method of estimating the heat history time of polyethylene that has been subjected to a heat history below the melting point, wherein the heat history temperature of polyethylene that has undergone this heat history is estimated, The melting curve of the received polyethylene was measured with a differential scanning calorimeter, and this melting curve shows at a temperature lower than the melting point.
Find the temperature that shows the peak on the low temperature side of the two peaks,
From these estimated heat history temperature and low temperature side peak temperature, the heat history time was obtained in advance with a known heat history of polyethylene,
A method for estimating heat history of polyethylene, which comprises estimating based on measurement data showing a relationship between heat history temperature and heat history time and a low temperature side peak temperature.