JP2019184251A - Strain measuring device at the time of resin curing and strain measuring method at the time of resin curing - Google Patents

Abstract

To provide a strain measuring device at the time of resin curing that can accurately measure a strain at the time of resin curing.SOLUTION: A strain measuring device at the time of resin curing in an embodiment comprises a strain gauge and a base member. The base member is of a rigid body on a first surface of which the strain gauge is affixed. The Young's modulus of the base member material is 7 GPa or lower.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a strain measuring device for resin curing and a strain measuring method for resin curing.

  In a molded product in which current-carrying parts made of metal commonly used in electrical equipment such as switchgears, bushings and transformers are molded with thermosetting resin, the electrical parts are placed in the mold and the thermosetting resin is placed in the mold. Performed with filling. When a large strain is generated in the process of curing the resin, the resin peels off on the surface of the embedded electrical component. If the resin is peeled off, partial discharge may occur when the electric component is used. Therefore, strain measurement during resin curing is required. However, with a commercially available strain gauge, it is difficult to accurately measure strain at the time of resin curing. The reason is that since the resin flows during the injection molding of the resin, the strain gauge is curved and the strain measurement direction cannot be fixed.

Japanese Patent Publication No. 60-13132

  The problem to be solved by the present invention is to provide a strain measuring device at the time of resin curing and a strain measuring method at the time of resin curing capable of accurately measuring the strain at the time of resin curing.

  The strain measurement apparatus for resin curing according to the embodiment includes a strain gauge and a base member. The base member is a rigid body having a strain gauge attached to the first surface. The Young's modulus of the material of the base member is 7 GPa or less.

The top view of the distortion measuring apparatus at the time of resin hardening of embodiment. Side surface sectional drawing in the F2-F2 line | wire of FIG. The bottom view of the distortion measuring device at the time of resin hardening of an embodiment. The 1st explanatory view of a strain measuring method. The 2nd explanatory view of a strain measuring method. The graph which shows the change of the various temperatures at the time of resin hardening.

  Hereinafter, a strain measuring device at the time of resin curing and a strain measuring method at the time of resin curing according to the embodiment will be described with reference to the drawings. In the present application, the X direction, the Y direction, and the Z direction are defined as follows. The X direction is a measurement direction of strain in a plane parallel to the strain gauge. The Y direction is a direction perpendicular to the strain measurement direction in a plane parallel to the strain gauge. The Z direction is the thickness direction of the strain gauge and is a direction perpendicular to the X direction and the Y direction.

FIG. 1 is a plan view of a strain measuring device 1 during resin curing according to an embodiment. 2 is a side cross-sectional view taken along line F2-F2 of FIG. FIG. 3 is a bottom view of the strain measurement apparatus 1 during resin curing according to the embodiment. As shown in FIG. 1, the strain measurement apparatus 1 at the time of resin curing according to the embodiment includes a strain gauge 2, a base member 10, and a string 16.
The strain gauge 2 is a commercially available strain gauge. As shown in FIG. 2, the strain gauge 2 includes a resistance foil 3, a base film 5, a protective film 6, and leads 4.

  The resistance foil 3 is formed of a metal material or the like whose electrical resistance value changes due to mechanical deformation. The resistance foil 3 is formed in a zigzag shape when viewed from the Z direction (see FIG. 1). The spelling of the resistance foil 3 includes a plurality of straight portions extending in the X direction. The strain gauge 2 measures the strain in the X direction in which the linear portion of the zigzag fold of the resistance foil 3 extends. The base film 5 and the protective film 6 are formed of a resin material having electrical insulation. The base film 5 and the protective film 6 cover the resistance foil 3 from both sides of the resistance foil 3. The lead 4 is connected to both ends of the resistance foil 3. The lead 4 is drawn out of the base film 5 and the protective film 6.

  The strain gauge 2 is bonded to the base member 10 with an adhesive 8. The adhesive 8 is a commercially available adhesive for strain gauge adhesion, and includes an epoxy resin and the like. The strain gauge 2 is bonded to the first surface (+ Z surface) 10 a in the thickness direction of the base member 10. The strain gauge 2 is disposed at the center of the base member 10 when viewed from the Z direction.

  As shown in FIG. 1, the base member 10 is formed in a rectangular plate shape. The base member 10 is a rigid body. In the present application, the rigid body means an object that is not easily deformed by an external force. That is, the rigid body is an object having high rigidity, which is a degree of difficulty of deformation against external force. Specifically, the rigidity is high enough to prevent deformation when the base member 10 is placed in the mold due to an external force accompanying the flow of the resin injected into the mold. The base member 10 has a thickness of, for example, 1 mm or more, thereby ensuring rigidity. The material of the base member 10 will be described later.

Concavities and convexities are formed on the second surface (−Z surface) 10 b opposite to the first surface 10 a of the base member 10. In the example of FIG. 2, a plurality of grooves (plural protrusions) 12 are formed as irregularities. As shown in FIG. 3, the plurality of grooves 12 extend in the Y direction. The unevenness may be a sandblast mark formed by sandblasting the second surface 10b.
A plurality of through holes 14 penetrating the base member 10 in the thickness direction are formed in the peripheral portion of the base member 10. In the example of FIG. 1, the through holes 14 are formed one by one at the four corners of the base member 10.

  The string 16 is passed through the through hole 14 and tied between the through hole 14 and the peripheral edge of the base member 10. As a result, the first end of the string 16 is connected to the base member 10. The second end portion of the string 16 extends outside the base member 10 from each of the plurality of through holes 14. The material of the string 16 will be described later.

The usage method of the strain measuring device at the time of resin hardening of embodiment is demonstrated.
FIG. 4 is a first explanatory view of a strain measuring method using the strain measuring device 1 during resin curing, and is a plan view of the second mold 20b of the mold 20. FIG. 5 is a second explanatory diagram of a strain measuring method using the strain measuring device 1 during resin curing, and is a cross-sectional view taken along line F5-F5 in FIG.

  The mold 20 is a mold for injecting a product material resin (thermosetting resin) that is a material of a resin product to mold the resin product. As shown in FIG. 5, for example, the mold 20 includes a first mold 20 a and a second mold 20 b. The mold 20 is configured by combining partial molds other than the first mold 20a and the second mold 20b depending on the shape of the resin product. A cavity 22 corresponding to the product shape is formed inside the mold 20. The cavity 22 is sealed by combining the first mold 20a and the second mold 20b. The first mold 20 a has a sprue 24 and a gate 25. The product material resin is injected from the outside of the mold 20 into the cavity 22 through the sprue 24 and the gate 25. A heating device (not shown) is disposed outside the mold 20. The heating device indirectly heats the product material resin injected into the cavity 22 by heating the mold 20.

FIG. 6 is a graph of changes over time in various temperatures. The solid line in FIG. 6 represents the temperature of the product material resin. The resin product is molded by the following procedure. The heat curing of the product material resin is performed in two stages: primary curing for changing the resin from a liquid to a gel-like body and secondary curing for exhibiting the characteristics of the resin. The secondary curing temperature is higher than the primary curing temperature.
The mold 20 is heated to the primary curing temperature T1 by a heating device. Product material resin is injected into the cavity 22. The product material resin is held inside the mold 20 until time t1. As a result, the product material resin is primarily cured. The first-cured product material resin is taken out from the mold 20. The released product material resin is introduced into a chamber (not shown) maintained at the secondary curing temperature T2. The product material resin is held in the chamber until time t2. As a result, the product material resin is secondarily cured (completely cured) to complete the resin product.

  The product material resin is distorted during the curing process. The magnitude of the strain of the product material resin depends on the shape and part of the resin product. The strain measurement device 1 at the time of resin curing of the embodiment measures strain at the time of curing of the product material resin at a specific portion and a specific direction in the cavity 22. That is, the product material resin is a strain measurement target resin.

  As shown in FIG. 4, the strain measuring device 1 is arranged in a specific part and a specific direction in the cavity 22 before the product material resin is injected. The position and direction of the strain measuring device 1 in the cavity 22 are fixed by the string 16. As described above, the first end of the string 16 is connected to the base member 10. The second end portion of the string 16 passes between the first mold 20a and the second mold 20b and is drawn out of the mold 20. The second end of the string 16 is sandwiched and held between the first mold 20a and the second mold 20b. A plurality of strings 16 extend from the base member 10 in all directions to hold the strain measuring device 1. Thereby, the position and direction in the cavity 22 of the strain measuring apparatus 1 are fixed. Note that the second end of the string 16 may be attached to the inner surface of the cavity 22.

  The product material resin is injected in a state where the strain measuring device 1 is arranged in a specific part and a specific direction in the cavity 22. The product material resin adheres to the strain measuring device 1 in the process of curing. As will be described later, the Young's modulus of the material of the base member 10 is smaller than the Young's modulus after curing of the product material resin. Therefore, the same distortion also occurs in the base member 10 following the distortion when the product material resin is cured. Since the strain gauge 2 is affixed to the base member 10, the strain gauge 2 can measure the strain when the product material resin is cured.

  As shown in FIGS. 2 and 3, a groove 12 extending in the Y direction is formed on the second surface 10 b of the base member 10. The product material resin enters the groove 12 in the process of curing. The groove 12 extending in the Y direction exhibits an anchor effect with respect to the X direction, which is the strain measuring direction of the strain gauge 2. Therefore, the followability of the base member 10 to the strain in the X direction when the product material resin is cured is improved. Therefore, the strain measuring apparatus 1 can accurately measure strain at the time of curing of the strain measurement target resin.

The material of the base member 10 will be described.
The Young's modulus after curing of the resin for general industrial use and semiconductor encapsulation is 8 to 20 GPa. Therefore, the base member 10 is formed of a material having a Young's modulus of 7 GPa or less. Thereby, the Young's modulus of the material of the base member 10 becomes smaller than the Young's modulus after curing of the strain measurement target resin. Therefore, the strain measuring apparatus 1 can accurately measure strain at the time of curing of the strain measurement target resin.

The Young's modulus of the strain measurement target resin varies during curing. Therefore, the Young's modulus of the material of the base member 10 is desirably 50% or less of the Young's modulus after curing of the strain measurement target resin. Thereby, the strain measuring apparatus 1 can measure the strain during curing of the strain measurement target resin in a wide range. For example, the strain measuring apparatus 1 can measure strain from primary curing to secondary curing of the strain measurement target resin.
As described above, the Young's modulus after curing of the resin for general industrial use and semiconductor encapsulation is 8 to 20 GPa. Therefore, the Young's modulus of the material of the base member 10 is desirably 4 GPa or less, which is 50% of 8 GPa.

The base member 10 is formed of a thermosetting resin such as an epoxy resin. The linear expansion coefficient of the resin of the base member 10 is larger than the linear expansion coefficient of the resistance foil of the strain gauge 2. Therefore, the strain gauge 2 measures the “apparent strain” due to the thermal expansion of the base member 10 during the thermosetting of the strain measurement target resin. At this time, it is necessary to correct the apparent distortion. Specifically, the true strain is calculated by subtracting the strain due to the thermal expansion of the base member 10 at the curing temperature of the strain measurement target resin from the apparent strain measured by the strain gauge 2.
However, the resin has a glass transition point. Before and after the glass transition point, the physical property values of the resin greatly change nonlinearly. If the glass transition point of the resin of the base member 10 is close to the curing temperature of the strain measurement target resin, it is difficult to correct the apparent strain.

  Therefore, the material of the base member 10 is selected so that the glass transition temperature of the material of the base member 10 is higher by 20 ° C. or more than the curing temperature (preferably secondary curing temperature) of the strain measurement target resin. Thereby, the physical property value change of the resin of the base member 10 becomes close to linear at the curing temperature of the strain measurement target resin. Therefore, the prediction accuracy of strain due to thermal expansion of the base member 10 at the curing temperature of the strain measurement target resin is improved. Thereby, since correction | amendment of an apparent distortion can be implemented correctly, the distortion at the time of hardening of distortion measurement object resin can be measured correctly.

A specific material of the base member 10 includes a cured product obtained from a main agent and a curing agent. Two-part resins are easy to handle at room temperature. The Young's modulus can be easily adjusted by adding inorganic particles such as silica.
The main ingredients are bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol E type epoxy resin, bisphenyl type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, polyether ether ketone, Any one or more materials selected from polycarbonate. Since these crystalline polymers do not have a mechanical inflection point up to the glass transition point, they are highly reproducible in measurements involving temperature changes.
The curing agent is at least one material selected from bisphenol A type cyanate, phenol novolac type cyanate, diaminodiphenylmethane, diaminodiphenylsulfone, and imidazole. The glass transition point of the resin can be adjusted by adjusting the curing agent or adding a curing accelerator.

The material of the string 16 will be described.
As described above, the position and direction in the cavity 22 of the strain measuring device 1 are fixed by holding the base member 10 with the plurality of strings 16. However, if the string 16 continues to hold the base member 10 in the process of curing the strain measurement target resin, the base member 10 cannot follow the strain of the strain measurement target resin. At this time, the strain gauge 2 cannot measure an accurate strain.

Therefore, the material of the string 16 is selected so that the softening temperature of the material of the string 16 is equal to or lower than the glass transition temperature of the strain measurement target resin. The two-dot chain line in FIG. 6 shows the change in the glass transition temperature of the resin. The glass transition temperature of the resin increases as the resin cures. The material of the string 16 is selected so that the softening temperature of the material of the string 16 is equal to or lower than the glass transition temperature at the time of primary curing of the strain measurement target resin. Thereby, the string 16 softens at the time of the primary curing of the product material resin, and the base member 10 is released from the holding. Therefore, the strain measuring apparatus 1 can accurately measure strain from primary curing to secondary curing of the strain measurement target resin.
Specific materials for the string 16 include nylon, polyvinylidene chloride, polypropylene, polyethylene, and polyester.

  As an example, the strain measuring apparatus 1 of the embodiment was produced. The base member 10 of the strain measuring device 1 of the embodiment is made of an epoxy resin and has a Young's modulus of 7 GPa. The thickness of the base member 10 is 1 mm. The strain measurement device 1 of the example was embedded in a dumbbell-type tensile test piece of a strain measurement target resin (epoxy resin), and a tensile test was performed. The Young's modulus was calculated from the stress calculated from the tensile load and the cross-sectional area of the tensile specimen and the strain measured by the strain gauge of the strain measuring device 1 of the example.

  As a comparative example, a strain measuring device in which a strain gauge was attached to a metal thin plate was produced. The metal thin plate of the strain measuring apparatus 1 of the comparative example has three types of materials, stainless steel, iron, and copper, and has a thickness of 0.2 mm. The strain measurement apparatus 1 of the comparative example was embedded in a dumbbell-type tensile test piece of a strain measurement target resin (epoxy resin), and a tensile test was performed. For the comparative example, the Young's modulus was calculated in the same manner as in the example.

  Table 1 shows the calculation results of Young's modulus of the examples and comparative examples.

  In order to verify the calculation result of Young's modulus, a tensile test was performed by attaching a strain gauge directly to the surface of a dumbbell-type tensile test piece of a strain measurement target resin (epoxy resin). From the stress calculated from the tensile load and the cross-sectional area of the tensile specimen and the strain measured by the strain gauge, the Young's modulus of the strain measurement target resin was calculated. As a result, the Young's modulus of the strain measurement target resin was 14 GPa.

  The calculation results of the Young's modulus in the examples of Table 1 coincide with 14 GPa, which is the verification result of the Young's modulus of the strain measurement target resin. The Young's modulus of the base member 10 in the strain measuring apparatus 1 of the example is 7 GPa, which is sufficiently smaller than the 14 GPa of the Young's modulus of the strain measurement target resin. Therefore, the same strain also occurs in the base member 10 following the strain of the strain measurement target resin. Since the strain gauge 2 measures the strain of the base member 10, it is considered that the Young's modulus of the strain measurement target resin was accurately calculated in the example.

  On the other hand, the calculation result of the Young's modulus in the comparative example of Table 1 is larger than 14 GPa which is the verification result of the Young's modulus of the strain measurement target resin. The Young's modulus of the metal thin plate in the strain measuring device 1 of the comparative example is larger than the 14 GPa of the Young's modulus of the strain measurement target resin. Therefore, the strain of the thin metal plate does not follow the strain of the strain measurement target resin, and the strain of the thin metal plate is reduced. Since the strain gauge 2 measures the strain of the thin metal plate, it is considered that the Young's modulus of the strain measurement target resin could not be accurately calculated in the comparative example.

  From the above, it was confirmed that the strain measuring apparatus 1 of the embodiment which is an example can measure an accurate strain of the resin.

  According to at least one embodiment described above, by having a rigid base member made of a material having a Young's modulus of 7 GPa or less, it is possible to accurately measure strain at the time of resin curing.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Strain measuring apparatus, 2 ... Strain gauge, 10 ... Base member, 10a ... 1st surface, 10b ... 2nd surface, 12 ... Groove (unevenness), 16 ... String, 20 ... Mold.

Claims (7)

Strain gauges,
The strain gauge has a rigid base member affixed to the first surface;
The Young's modulus of the material of the base member is 7 GPa or less,
Strain measuring device for resin curing. Strain gauges,
The strain gauge has a rigid base member affixed to the first surface;
The Young's modulus of the material of the base member is 50% or less of the Young's modulus after curing of the strain measurement target resin.
Strain measuring device for resin curing. The glass transition temperature of the material of the base member is 20 ° C. or more higher than the curing temperature of the strain measurement target resin,
The distortion measuring apparatus at the time of resin hardening of Claim 1 or 2. The base member has irregularities on a second surface opposite to the first surface;
The distortion | strain measuring apparatus at the time of resin hardening of any one of Claim 1 to 3. Having a string connected to the base member;
The softening temperature of the material of the string is equal to or lower than the glass transition temperature of the strain measurement target resin.
The distortion | strain measuring apparatus at the time of resin hardening of any one of Claim 1 to 4. The base member includes a cured product obtained from a main agent and a curing agent,
The main ingredients are bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol E type epoxy resin, bisphenyl type epoxy resin, phenol novolac type epoxy resin, cresol novolac type epoxy resin, polyether ether ketone. , Any one or more materials selected from polycarbonate,
The curing agent is one or more materials selected from bisphenol A type cyanate, phenol novolac type cyanate, diaminodiphenylmethane, diaminodiphenylsulfone, and imidazole.
The distortion | strain measuring apparatus at the time of resin hardening of any one of Claim 1 to 5. A strain gauge, a rigid base member to which the strain gauge is attached, and a string connected to the base member, and the Young's modulus of the material of the base member is determined after the resin to be strain-measured is cured. Using a strain measurement device during resin curing that is 50% or less of the Young's modulus of
The strain measuring device is disposed in a mold, the position and direction of the strain measuring device in the mold is fixed by the string, and the strain measurement target resin is injection-molded in the mold, Measure strain at the time of curing of the strain measurement target resin,
Strain measurement method during resin curing.

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