JP2015190847A - Evaluation method of crosslinking degree of macromolecular polymer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method capable of safely and easily measuring the crosslinking degree of a macromolecular polymer.SOLUTION: In the evaluation method of the crosslinking degree of a macromolecular polymer crosslinked with a radiation ray or a crosslinking agent, a storage elastic modulus is measured by dynamic viscoelasticity measurement in a temperature range from a room temperature to a fusion temperature, a calibration curve is obtained on the basis of the correlation between the storage elastic modulus obtained from the result and a gel fraction obtained by the measuring method of the crosslinking degree of JIS C 3005, and then the storage elastic modulus is measured. Thus, the crosslinking degree of a macromolecular polymer can be evaluated without measuring the gel fraction.

Description

The present invention is a method for evaluating the degree of cross-linking of polyolefin resins such as polyethylene and polypropylene, which are polymer polymers generally used in electrical products, and is a novel polymer that can be safely and simply evaluated. The present invention relates to a method for evaluating the degree of crosslinking of a polymer.

Because of its excellent electrical characteristics and excellent heat resistance and solvent resistance, polyolefin resins such as polyethylene and polypropylene have been used in various applications for electrical products. These high molecular polymers can generally be crosslinked by radiation crosslinking by electron beam / gamma ray irradiation or chemical reaction (crosslinking reaction) with a crosslinking agent, a coupling agent, a peroxide or the like. Here, it is known that heat resistance and mechanical properties at high temperatures are greatly improved by crosslinking a polymer. That is, since the performance of the resin varies greatly depending on the progress of the crosslinking reaction, it is important to accurately evaluate the degree of crosslinking of the polymer.
In general, the degree of crosslinking of a polymer is evaluated by a test method called “gel fraction” (see Non-Patent Document 1). This method is briefly described. Heating xylene as a deleterious substance and organic solvent to 110 ° C., immersing and holding a polymer sample to be evaluated for 24 hours, then removing the sample and drying it at a temperature of 100 ° C. and a vacuum degree of 1.3 kPa or less for 24 hours or more. .
Here, the mass M2 of the dried polymer sample was measured, and as the mass M1 of the polymer sample before being immersed in xylene, the degree of cross-linking was M2 / M1, which is the ratio of M1 to M2, expressed as “gel fraction. ". That is, when the polymer is dissolved in a solvent, the portion that remains without being dissolved is defined as a gel (the cross-linked portion remains as a gel), and the ratio (percentage) between the mass of the gel portion and the mass before being dissolved in the solvent is expressed as “ The degree of progress of crosslinking is evaluated as “gel fraction”.
The above-described method for measuring the gel fraction has a problem in that it requires a harmful deleterious substance and xylene, which is an organic solvent, and takes more than two days for the measurement.

Rubber / plastic insulated wire test method JIS C 3005: 2000 4.25

As a method for measuring the degree of cross-linking of high-molecular polymers that are generally used in electrical products, the degree of cross-linking of high-molecular polymers can be measured safely and easily, eliminating the problems of general gel fraction measurement methods. The evaluation method was desired.

  The polymer polymer evaluation method provided by the present invention is a method for evaluating the degree of cross-linking of a polymer polymer cross-linked with radiation or a cross-linking agent, and storage elasticity is measured by dynamic viscoelasticity measurement in a temperature range from room temperature to melting temperature. This is a method for evaluating the degree of cross-linking of a high molecular polymer that obtains a calibration curve from the correlation between the storage elastic modulus obtained from this result and the gel fraction obtained by the method for measuring the degree of cross-linking of JIS C 3005. .

  ADVANTAGE OF THE INVENTION According to this invention, the evaluation method of the crosslinking degree of the high molecular polymer which can measure the crosslinking degree of the high molecular polymer generally used with an electrical product safely and simply is provided.

Measurement results of storage modulus of polyethylene resin Figure showing the relationship between storage modulus and gel fraction The figure which showed the relationship between the storage elastic modulus and gel fraction of the high density polyethylene of an Example

In order to solve the problems in the above-described measurement method of the gel fraction, which is a method for measuring the degree of crosslinking of a high-molecular polymer such as polyethylene or polypropylene, which is conventionally used for electronic components, We have intensively studied a method for evaluating the degree of crosslinking of a novel polymer that can be measured safely and easily.
As a result, the storage elastic modulus of a polymer, which is one of the viscoelastic bodies, is measured by dynamic viscoelasticity measurement (DMA: Dynamic Mechanical Analysis). Thus, the present inventors have found that this is a method capable of simply and safely evaluating the degree of cross-linking of a high molecular weight polymer, thereby completing the present invention.

First, the viscoelastic body and the storage elastic modulus will be described.
In general, a viscoelastic body is a substance having both viscous and elastic properties.
Elasticity is a property (Hook's law) in which a certain strain occurs when stress is applied, and when the stress is removed, the strain completely returns to its original state and a proportional relationship is established between the stress and strain.
Viscosity is the property that when a stress is applied, deformation occurs at a constant strain rate, and when the stress is removed, the strain remains constant without recovery, and a proportional relationship is established between the stress and strain rate (Newton's law) It is.
The coefficient proportional to the component stored inside the substance of the energy generated by stress and strain volume is called the storage elastic modulus E (Pa), and the coefficient proportional to the component diffusing as heat to the outside of the substance is the loss elastic modulus E (Pa). The (complex) elastic modulus E (Pa) is defined as the vector sum of the storage elastic modulus E (Pa) and the loss elastic modulus E (Pa).
A viscoelastic body such as a high molecular polymer becomes softer from the hard glass state to the glass transition temperature as the temperature increases. When the temperature further rises to near the melting point, it becomes liquid.
When the storage elastic modulus (unit: Pa) is taken on the vertical axis, it becomes rubbery and decreases in a temperature range that has been decreasing with temperature. The temperature near the lowest minimum temperature is close to the melting point.
The dynamic viscoelastic temperature distribution curve of a polymer solid is divided into a glass region, a transition region, and a rubber-like flat region with a glass transition temperature as a boundary.
In general, the storage elastic modulus is high in the glass region, and greatly decreases in the vicinity of the melting point.
In dynamic viscoelasticity measurement (DMA), a sample is deformed (strained), a response force (stress) is obtained from the sample, and the strain is measured by an optical coder to obtain the deformation.
When the storage elastic modulus is high, the restoring force of the sample is strong, it decreases as the temperature increases, and rapidly decreases near the melting point. That is, it shows that the high molecular polymer of the sample was softened.
It can be said that the higher the degree of cross-linking, the lower the storage elastic modulus at the melting point compared to room temperature.
By measuring the storage elastic modulus Em in the vicinity of the melting point and the storage elastic modulus Er in the vicinity of room temperature, the degree of cross-linking of the polymer can be evaluated. That is, when the crosslinking reaction is not progressing (the degree of crosslinking is low), the gel fraction is small, and the ratio Er / Em between the storage elastic modulus Em at the melting point and the storage elastic modulus Er at room temperature (20 ° C.) is also small. As the crosslinking reaction proceeds (the degree of crosslinking is high) and the gel fraction increases, the ratio Er / Em between the storage elastic modulus Em at the melting point and the storage elastic modulus Er at room temperature (20 ° C.) also increases.
Considering the above, using the same sample, the storage elastic modulus measurement by dynamic viscoelasticity measurement (DMA) and the gel fraction measurement by JIS C 3005: 2000 4.25 are performed, and the storage elastic modulus ratio and the gel content are measured. The correlation with rate was examined.
First, storage elastic modulus measurement by dynamic viscoelasticity measurement (DMA) will be described.
Samples of polyethylene resin cross-linked by irradiation with three levels of radiation and pre-irradiation polyethylene resin are prepared as measurement samples, and stored in the temperature range from room temperature to 170 ° C using TY Instruments DMAQ800. The elastic modulus was measured.
FIG. 1 shows the measurement results.
The radiation-crosslinked polyethylene resin has a high storage elastic modulus of 3000 to 5000 MPa in the vicinity of the melting point (135 to 140 ° C.). Moreover, the uncrosslinked polyethylene resin shows a value of 200 to 400 MPa, which is one digit lower.
When measuring the storage elastic modulus by dynamic viscoelasticity measurement (DMA), 1 to 10 Hz is used as the measurement frequency, and 1, 3 and 5 Hz are desirable accurately.
As for the temperature raising condition, if the frequency is reduced, the accuracy is higher when the temperature raising rate is also reduced.
Considering the measurement time and measurement accuracy, it is desirable to set it to 5 ° C./min or less.
In addition, there are tensile, compression, shear, double-end beam bending, cantilever beam bending, and free support three-point bending as methods for applying stress under the measurement conditions, but measurement is performed by cantilever beam bending without applying extra force to the sample. Is desirable.
The storage elastic modulus Em near the melting point (135 ° C.) of the polyethylene resin and the storage elastic modulus Er near the room temperature are read, and the ratio Er / Em between the storage elastic modulus at the melting point and the storage elastic modulus at the room temperature (20 ° C.) is calculated.
Next, the gel fraction measurement according to JIS C 3005: 2000 4.25 will be described. The gel fraction is generally a technique for measuring the degree of curing of a high molecular polymer, that is, the degree of crosslinking.
The mass M1 of the sample before being immersed in the organic solvent xylene was measured, the mass M2 of the sample after the test was measured, the ratio M2 / M1 between them was calculated, and the degree of crosslinking X (%) was determined as the gel fraction = M2. Expressed as / M1 × 100.
The sample was immersed and held in xylene at 110 ° C. for 24 hours, and the sample was held sealed in a container so that xylene did not volatilize. After 24 hours, the sample was taken out in a fume hood and further dried at 100 ° C. and 1.3 kPa or less for 24 hours using a vacuum dryer.
Thereafter, the weight of the resin after drying was measured, and the resin remaining without being dissolved was measured as gel fraction gel fraction = M2 / M1 × 100 as compared with the resin weight before dipping in xylene.
As described above, it took substantially 3 days to measure one sample.

  “Gel fraction M2 / M1 × 100” obtained by gel fraction measurement according to JIS C 3005: 2000 4.25 with “ratio of storage elastic modulus at melting point to storage elastic modulus at room temperature Er / Em” on the horizontal axis Is plotted on the vertical axis and shown in FIG.

As apparent from FIG. 2, there is a correlation between the “ratio of storage elastic modulus at melting point to storage elastic modulus at room temperature Er / Em” and “gel fraction M2 / M1 × 100”, and the degree of crosslinking of the polymer. As an evaluation method, it can be seen that it is effective to measure the storage elastic modulus of a high molecular polymer by dynamic viscoelasticity measurement (DMA).
Hereinafter, the embodiment will be described in detail.

As a sample, high-density polyethylene (density 960 kg / m ³ ) having a melting point of 135 ° C. was used.
This resin was molded into a sheet having a thickness of 0.6 mm using a hot press at 160 ° C.
As the crosslinking, radiation crosslinking using an electron beam was selected.
As the electron beam accelerator, EPS-3000 manufactured by NHX Corporation was used.
As radiation crosslinking conditions, an irradiation dose of 250 kGy with an acceleration voltage of 3000 kV and a current of 20 mA and an irradiation with 500 kGy were obtained.

Dynamic viscoelasticity measurement (DMA) was performed on three types of samples, the two irradiated samples and the unirradiated sample. As a viscoelasticity measuring apparatus, TA Instruments (DMAQ800 type) was used. The sample size was cut into a length of 30 mm, a width of 5 mm, and a thickness of 0.5 mm, and attached to the apparatus with three points. As conditions for applying stress to the element, the frequency was 0.5 Hz, the temperature rising rate was 1 ° C./minute, and the measurement temperature was measured from room temperature to 170 ° C. As a result, the storage elastic modulus ratio Er between the melting point (135 ° C.) and room temperature (20 ° C.) / Em was 0.11 for 250 kGy irradiation and 0.13 for 500 kGy irradiation. The unirradiated one was 0.023.

Further, the degree of cross-linking of these three types of samples was measured with a gel fraction of JIS C 3005.
The sample was immersed and held in xylene at 110 ° C. for 24 hours, and the sample was held sealed in a container so that xylene did not volatilize. After 24 hours, the sample was taken out in a fume hood and further dried at 100 ° C. and 1.3 kPa or less for 24 hours using a vacuum dryer.
Thereafter, the weight of the resin after drying was measured, and the resin remaining without being dissolved was measured as a gel fraction as compared with the weight of the resin before being immersed in xylene.
As described above, it took substantially 3 days to measure one sample.

  As a result, the gel fraction was 85% when irradiated with 250 kGy and 94% when irradiated with 500 kGy. The unirradiated material was 20%.

  The above measurement results are shown in FIG. The process of cross-linking by radiation irradiation is also recognized from the correlation between the storage elastic modulus ratio Er / Em and the gel fraction, and in order to sufficiently cross-link this high-density polyethylene, the storage at which the gel fraction is 85% or more. It can be seen that the electron beam irradiation dose with an elastic modulus ratio Er / Em of 0.13 is required to be 250 kGy or more.

Claims (1)

This is a method for evaluating the degree of cross-linking of a polymer polymer cross-linked with radiation or a cross-linking agent, and the storage elastic modulus is obtained by measuring the storage elastic modulus by dynamic viscoelasticity measurement in the temperature range from room temperature to the melting temperature. And a calibration curve is obtained from the correlation between the gel fraction obtained by the method for measuring the degree of crosslinking according to JIS C 3005, and a method for evaluating the degree of crosslinking of a polymer.