JP2008073865A - Foam evaluation method for injection foam molding - Google Patents

Abstract

The present invention provides a method for obtaining an average volume of bubbles contained in an injection-molded product to determine the degree of increase in the diameter of the bubbles contained in the injection-molded product, and a method for obtaining the generation point and frequency of bubbles. .
An average volume of bubbles contained in an injection molded product obtained by injection molding a resin composition containing a resin and a foaming component is determined by X-ray computer tomography, and the position and average volume of the injection molded product are determined. The relationship is represented by an approximate curve, and the degree of increase in bubble diameter is determined using the differential equation of the approximate curve. Also, the number density of bubbles contained in the injection-molded product is obtained by X-ray computer tomography, the relationship between the position and number density in the injection-molded product is represented by an approximate curve, and the bubble generation start point is obtained using the approximate curve. Further, the bubble generation frequency is obtained using the differential equation of the approximate curve.
[Selection] Figure 1

Description

The present invention relates to a method for evaluating foaming of an injection molded article. More specifically, the present invention relates to a method for obtaining an average volume of bubbles contained in an injection-molded product by X-ray computer tomography and obtaining a degree of increase in the diameter of bubbles contained in the injection-molded product,
Further, the present invention relates to a method for obtaining the number density contained in the injection molded article by X-ray computer tomography and determining the generation point and frequency of bubbles contained in the injection molded article.

  Conventionally, a method of injection molding a resin composition containing a resin and a foaming component has been used to improve the rigidity, appearance, or weight of an injection molded body, and evaluate the foaming characteristics of the injection molded body. How to do is known.

  For example, in Japanese Patent Laid-Open No. 2000-61982, as a means for improving the settling and surface roughness of a polypropylene resin foam, after inserting the polypropylene resin foam into an injection mold and clamping the mold, the polypropylene resin foam There is described a polypropylene resin foam composite molded article which is manufactured by flowing a molten resin on the surface of the resin layer in a specific method and has an average cell diameter of 200 μm or less in the surface layer portion from the surface to 0.5 mm. As a method for measuring the average cell diameter, a method is described in which the surface layer portion of the foam is magnified 50 to 100 times with SEM, and the largest cell cross section in the longitudinal direction is photographed and measured.

  Japanese Patent Laid-Open No. 2001-288293 includes a thermoplastic resin and a layered silicate as main components as means for uniformly dispersing uniform fine foam cells in a thermoplastic resin foam, and has an average cell diameter and foam. A thermoplastic resin foam having a specific relationship in magnification is described. As a method for measuring the foam cell diameter, a method is described in which the foam is observed with a secondary electron reflection electron microscope, and the average of 50 observed foam cells is used as the foam cell diameter.

  Furthermore, in Japanese Patent Application Laid-Open No. 2003-313352, as a means for making the foam structure contained in the polyamide foam uniform, each of the density and hardness is in a specific range, and a foamed polyamide having a foam size of 20 to 200 μm. The body is listed. As a method for measuring the bubble size of the foam, a method is described in which a cross-section of the foam is photographed with a scanning electron microscope, and the average bubble size is calculated from the size measured on the photograph and the magnification at the time of photographing. Yes.

Japanese Unexamined Patent Publication No. 2000-61982 JP 2001-288293 A JP 2003-313352 A

  However, even in the method described in the above publications, it is difficult to elucidate phenomena related to foaming characteristics such as the degree of increase in the diameter of bubbles contained in an injection-molded product, the generation point and generation frequency of bubbles, and the improvement Was demanded.

An object of the present invention is to provide a method for obtaining an average volume of bubbles contained in an injection-molded body by using X-ray computer tomography and obtaining a degree of increase in the diameter of the bubbles contained in the injection-molded body. Yes,
It is another object of the present invention to provide a method for determining the generation point and generation frequency of bubbles contained in an injection molded article using X-ray computer tomography.

In light of such circumstances, the present inventors have found that the present invention can solve the above-mentioned problems as a result of intensive studies, and have completed the present invention.
That is, one aspect of the present invention is
An injection-molded article obtained by injection-molding a resin composition containing a resin and a foam component by performing the operation (1-2) following the operation (1-1) described below. This relates to a method for determining the degree of increase in the diameter of the bubbles contained in.
(1-1) Define the coordinate axis of the injection molded body with 0 as the end of the injection molded body corresponding to the gate portion and 100 as the flow end in the resin flow direction, and injection molding between position 0 to position 100 of the coordinate axis. The average volume of bubbles contained in the body is obtained by X-ray computed tomography.
(1-2) The relationship of the average volume with respect to the coordinate axis position of the injection molded body is represented by an approximate curve, a differential expression of the approximate curve is obtained, and the gradient of the differential expression with respect to the position of the coordinate axis of the injection molded body is given to the injection molded body. Calculated as the degree of increase in the diameter of the contained bubbles.

The second aspect of the present invention is
An injection molded article obtained by injection molding of a resin composition containing a resin and a foaming component is subjected to the operation (2-2) following the operation (2-1) below. This relates to a method for obtaining the generation point of bubbles contained in the.
(2-1) The coordinate axis is defined in the injection molded body where the end of the injection molded body corresponding to the gate portion is 0 and the flow end in the resin flow direction is 100, and the injection molding between position 0 to position 100 of the coordinate axis is performed. The number density of bubbles contained in the body is obtained by X-ray computed tomography.
(2-2) The relationship of the number density with respect to the position of the coordinate axis of the injection molded body is represented by an approximate curve, and the position of the injection molded body where the number density is 0 in the approximate curve is obtained as a bubble generation start point.

And three of the present invention is
An injection molded article obtained by injection molding a resin composition containing a resin and a foaming component is subjected to the operation (3-2) following the operation (3-1) below. This relates to a method for determining the frequency of occurrence of bubbles contained in the.
(3-1) The coordinate axis is defined in the injection molded body with the end of the injection molded body corresponding to the gate portion as 0 and the flow end in the resin flow direction as 100, and the injection molding between position 0 to position 100 of the coordinate axis. The number density of bubbles contained in the body is obtained by X-ray computed tomography.
(3-2) The relationship between the number density of bubbles with respect to the position of the coordinate axis of the injection molded body is expressed by an approximate curve, a differential expression of the approximate curve is obtained, and the slope of the differential expression with respect to the position of the coordinate axis of the injection molded body is expressed in unit time. Obtained as the frequency of occurrence of bubbles.

Furthermore, the present invention provides:
Regarding the spiral flow injection molded article, according to the method of the present invention, the method relates to a method for obtaining a degree of increase in the diameter of bubbles contained in the spiral flow injection molded article,
The spiral flow injection molded article relates to a method for obtaining the generation point of bubbles contained in the spiral flow injection molded article by the two methods of the present invention,
The spiral flow injection molded article relates to a method for determining the occurrence frequency of bubbles contained in the spiral flow injection molded article by the three methods of the present invention.

  According to the method of the present invention, the degree of increase in the diameter of the bubbles contained in the injection-molded product can be obtained by obtaining the average volume of the bubbles contained in the injection-molded product using X-ray computed tomography. Moreover, the generation | occurrence | production start point and generation frequency of the bubble contained in an injection molded object can be calculated | required by obtaining the number density of the bubble contained in an injection molded object using X-ray computer tomography.

  The position in the injection-molded product used in the present invention is determined by defining the coordinate axis of the injection-molded product with 0 as the end of the injection-molded product corresponding to the gate portion and 100 as the flow end in the resin flow direction.

  The injection molded body is one in which the resin is injected into the mold at a constant pressure, and the injection amount of the resin is proportional to the injection speed, and the injection amount is proportional to the length of the injection molded body in the resin flow direction. Define the position of the injection molded body by defining the end of the injection molded body corresponding to the part as 0 and the flow end in the resin flow direction as 100, and quantifying or standardizing the length of the injection molded body in the resin flow direction By doing so, the length can be converted into time.

  The measurement position of the injection molded body that performs X-ray tomography measurement may be within the range of the position 0 and the position 100 of the coordinate axis. The number of measurement positions is preferably as long as the measurement time does not become large, and the interval between the measurement positions is preferably as fine as possible.

  The X-ray tomography measurement is performed with a current value and a voltage value at which a sufficient contrast between the resin and bubbles can be obtained. Further, the magnification of the obtained observation image is a magnification at which the bubbles are clearly observed within the range of the bubble particle size of interest. When the number of bubbles detected by increasing the magnification decreases, the same measurement is performed by changing several measurement fields in the immediate vicinity of the measurement position, and the average processing of a plurality of obtained data is performed. It is preferable to improve the accuracy.

  The software used to obtain the bubble diameter should be software that can binarize the resin part and bubble part of the photographic data obtained by the X-ray tomography measurement and obtain the bubble volume and bubble number in the measurement area. It ’s fine.

Plot the average volume or number density against the position of the injection-molded body, express the relationship between the coordinate axis position of the injection-molded body and the average volume with an approximate curve, find the differential equation of the approximate curve, and calculate the slope of the differential equation The software you want,
The relationship between the position of the coordinate axis of the injection molded body and the number density is represented by an approximate curve, the position of the injection molded body where the number density is 0, the differential equation of the approximate curve is obtained, and the software for obtaining the slope of the differential equation is Commercially available software may be used.
A function used for obtaining an approximate curve may be a quadratic function, an exponential function, or the like depending on the accuracy of fitting.

[Composition of injection molded product]
Table 1 below shows the types of propylene-based resins used in the injection-molded products, the foaming components, and their compositions.

ＡＺ８６４Ｅ４およびＡＵ５６１Ｅ１は、住友化学（株）製ポリプロピレン系重合体である。

AZ864E4 and AU561E1 are polypropylene polymers manufactured by Sumitomo Chemical Co., Ltd.

[Production of Propylene Polymer A]
The propylene polymer A was produced as follows.
A mixture of 92 parts by weight of homopolymer and 8 parts by weight of 2.5 dimethyl-2.5 di (tertiary butyl peroxy) hexene was 0.8 per 100 parts by weight of propylene ethylene-α olefin block copolymer AY564 manufactured by Sumitomo Chemical Co., Ltd. The composition which added the weight part, and adjusted the molecular weight with the barrel temperature of 250 degreeC, the extrusion amount of 30-50 kg / hr, and the screw rotation speed at 350 rpm using the twin-screw kneading extruder (TEX44SS 30BW-2V type made by Nippon Steel Works). 25 parts by weight of ethylene-octene copolymer ENGAGE8407 manufactured by DuPont Dow Elastomer Co., Ltd. was added to 75 parts by weight of this resin, and a twin-screw kneading extruder (TEX44SS 30BW-2V manufactured by Nippon Steel Works) was used. , Barrel temperature 200 ° C, extrusion rate 30-50kg / hr, screw rotation speed 350 Obtained by mixing at rpm.

[Method of mixing propylene polymer and foaming agent]
It knead | mixes each of the propylene-type polymer of Examples 1-3 so that the content of a chemical foaming agent may be 20 to 80 weight%, it was set as the masterbatch, and this masterbatch was used for the propylene-type polymer of Examples 1-3. Each blended further.

[Spiral flow injection molding method]
Spiral flow molding was performed as an injection molding method. As a molding machine, Neomat 5151/150 manufactured by Sumitomo Heavy Industries, Ltd. was used. A spiral flow mold was mounted on this molding machine, and molding was performed under the conditions of a barrel temperature of 200 ° C., a mold temperature of 50 ° C., an injection pressure of 40 kgG, and a cooling time of 30 seconds to obtain a spiral flow injection molded body.

[Production method of injection foam molding]
The injection foam molding was prepared by the following method.
A spiral flow injection mold having a disk-shaped cavity having a thickness of 2 mm and a smooth cavity surface was attached to an in-line type injection machine having a theoretical injection capacity of 750 cc. About 130 g was measured at an injection molding machine barrel temperature of 200 ° C. The mold temperature was kept at 50 ° C., and the molten resin was injected and filled in the mold in about 1.5 seconds. The mold opening was started in the direction of increasing the cavity thickness 1 second after the completion of filling, and the cavity opening operation was stopped when the cavity thickness reached 3.6 mm after about 2 seconds. The foam was cooled for 30 seconds while maintaining this state, and then the mold was opened to obtain a spiral flow injection foam molded body of a polypropylene resin having a thickness of 3 mm.

[X-ray computed tomography imaging method]
The imaging conditions are not particularly limited as long as bubbles of a particle volume in a range of interest in the molded body can be clearly observed. In this embodiment, the imaging conditions are approximately the same as the resolution of an X-ray computed tomography (hereinafter, X-ray CT) apparatus. The measurement was performed under high-magnification imaging conditions in which bubbles having a diameter of 10 μm could be observed. The apparatus used, the measurement conditions, and the measurement area of this example were as follows.

[Device used]
Shimadzu X-ray CT system SMX-130CT
〔Measurement condition〕
Optical system X-ray source-sample distance 60mm
X-ray source-detector distance 570mm
Current value 96μA, voltage value 39kV
Fine mode Cone CT mode (A 1.5 mm wide region was observed.)

[Measurement area]
The measurement sample of the bubble distribution of the spiral flow injection molding is about 2 to 3 mm in the range from the position 0 of the injection molding corresponding to the gate part of the spiral flow injection molding machine to the position 100 of the flow end in the resin flow direction. A section of width was cut out. The measurement was performed on the central portion (observation area volume is about 8 mm ³ ) of the cut-out spiral flow injection molded body.

[Analysis of data obtained by X-ray CT measurement]
In this embodiment, 3D trabecular structure analysis software “3D bone for Win NT / 2000” sold by Ratok System Engineering Co., Ltd. was used. Using this software, the image obtained by CT measurement was binarized to select the region of the foam pores. Then, a minute void having a diameter of 10 μm or less in the selected region was erased as noise, and the remaining bubble diameter was analyzed to obtain the average volume and the number of bubbles in the analysis field.

Between the position 0 of the injection molded body corresponding to the gate portion and the position 100 of the flow end in the resin flow direction, with respect to at least six positions of the spiral flow injection molded body of various resin compositions containing foaming components, X-ray CT measurement and analysis of bubbles were performed, and using software Igor Pro sold by Hulinks Co., Ltd., FIG. 1, FIG. 2, and FIG. make,
A fitting function: y = 0.007 × exp (0.078 × (x−99.0)) is obtained as an approximate curve from FIG.
From FIG. 2, a fitting function: y = 0.0003 × exp (0.011 × (x−51.6)) + 0.002 is obtained as an approximate curve,
From FIG. 3, the fitting function: y = 0.0038 × exp (0.017 × (x + 127.6)) − 0.005 was obtained as an approximate curve.
The respective fitting functions are shown in FIGS. 1 to 3, respectively.

  FIG. 4 shows the differential equations of the fitting functions obtained as approximate curves in FIGS. 1 to 3. In each differential equation shown in FIG. 4, the gradient of each differential equation with respect to each position of the coordinate axis of the spiral flow injection molded body represents the degree of increase in the bubble diameter.

With the position of the injection molded body as the horizontal axis and the number density as the vertical axis, FIG. 5, FIG. 6 and FIG.
From FIG. 5, a fitting function: 19.1 × exp (0.061 × (x−93.2)) − 3.0 is obtained as an approximate curve,
The fitting function: 35.6 × exp (0.0066 × (x−62.7)) − 20.3 is obtained from FIG. 6 as an approximate curve, and the fitting function: 50.4 × exp as an approximate curve from FIG. (0.017x (x-65.2))-31.6 was determined.
The value of the X-axis intercept of the fitting function obtained as an approximate curve in FIGS. 5 to 7 is the position of the bubble generation start point, and Table 2 shows the bubble generation start point.

  Further, FIG. 8 shows the differential equations of the fitting functions obtained as the approximate curves in FIGS. In each differential expression shown in FIG. 8, the slope of each differential expression with respect to each position of the coordinate axis of the spiral flow injection molded body represents the frequency of bubble generation.

[Foaming characteristics of injection foam moldings]
The characteristics of the obtained spiral flow injection molded articles of Examples 1 to 3 are summarized in Table 2. As shown in Table 2, by the method of the present invention, it is possible to quantitatively determine the degree of increase in the diameter of bubbles contained in the injection-molded product, the generation start point and generation frequency of bubbles.

  As described above in detail, according to the method of the present invention, by using X-ray computed tomography, by obtaining the average volume of the bubbles contained in the injection molded article, the diameter of the bubbles contained in the injection molded article is obtained. The degree of increase can be determined, and by using X-ray computed tomography to obtain the number density of bubbles contained in the injection molded article, the generation start point and frequency of bubbles contained in the injection molded article are obtained. Can be requested.

  In addition, different resin compositions are injection molded under the same conditions to create an injection molded body, and by comparing the degree of increase in the bubble diameter of each injection molded body, the bubble generation start point and the bubble generation frequency, The foaming characteristics of different resin compositions can be examined.

  Also, for example, using the same resin composition, injection molded products are molded under different injection molding conditions, and the degree of increase in bubble diameter, bubble generation start point, and bubble generation frequency of each injection molded product are compared. By doing so, it is possible to examine the influence of different injection molding conditions on the injection molded body. And the molding conditions required in order to make each foaming state of a different resin composition approach the same foaming state can also be examined.

Relationship between the position and average volume of the injection-molded body of Example 1 and an approximate curve Relationship between the position of the injection molded body of Example 2 and the average volume, and an approximate curve Relationship between the position of the injection molded body of Example 3 and the average volume, and an approximate curve Differential equation of approximate curve of position and average volume Relationship between the position of the injection-molded body of Example 1 and the number density of bubbles and an approximate curve Relationship between the position of the injection-molded product of Example 2 and the number density of bubbles and an approximate curve Relationship between the position of the injection-molded body of Example 3 and the number density of bubbles and an approximate curve Differential equation of approximate curve of position and bubble number density

Claims (6)

An injection-molded article obtained by injection-molding a resin composition containing a resin and a foam component by performing the operation (1-2) following the operation (1-1) described below. The method of calculating | requiring the grade of the increase in the diameter of the bubble contained in.
(1-1) Define the coordinate axis of the injection molded body with 0 as the end of the injection molded body corresponding to the gate portion and 100 as the flow end in the resin flow direction, and injection molding between position 0 to position 100 of the coordinate axis. The average volume of bubbles contained in the body is obtained by X-ray computed tomography.
(1-2) The relationship of the average volume with respect to the position of the coordinate axis of the injection molded body is represented by an approximate curve, a differential expression of the approximate curve is obtained, and the slope of the differential expression with respect to the position of the coordinate axis of the injection molded body is defined in the injection molded body. Calculated as the degree of increase in the diameter of the contained bubbles. An injection molded article obtained by injection molding of a resin composition containing a resin and a foaming component is subjected to the operation (2-2) following the operation (2-1) below. Of determining the generation point of bubbles contained in the water.
(2-1) The coordinate axis is defined in the injection molded body where the end of the injection molded body corresponding to the gate portion is 0 and the flow end in the resin flow direction is 100, and the injection molding between position 0 to position 100 of the coordinate axis is performed. The number density of bubbles contained in the body is obtained by X-ray computed tomography.
(2-2) The relationship of the number density with respect to the position of the coordinate axis of the injection molded body is represented by an approximate curve, and the position of the injection molded body where the number density is 0 in the approximate curve is obtained as a bubble generation start point. An injection molded article obtained by injection molding a resin composition containing a resin and a foaming component is subjected to the operation (3-2) following the operation (3-1) below. Of determining the frequency of occurrence of bubbles contained in the water.
(3-1) The coordinate axis is defined in the injection molded body with the end of the injection molded body corresponding to the gate portion as 0 and the flow end in the resin flow direction as 100, and the injection molding between position 0 to position 100 of the coordinate axis. The number density of bubbles contained in the body is obtained by X-ray computed tomography.
(3-2) The relationship between the number density of bubbles with respect to the position of the coordinate axis of the injection molded body is expressed by an approximate curve, a differential expression of the approximate curve is obtained, and the slope of the differential expression with respect to the position of the coordinate axis of the injection molded body is expressed in unit time. Obtained as the frequency of occurrence of bubbles. A method for obtaining a degree of increase in the diameter of bubbles contained in a spiral flow injection molded article by the method according to claim 1 for the spiral flow injection molded article. A method for obtaining a generation point of bubbles contained in a spiral flow injection molded article by the method according to claim 2 for the spiral flow injection molded article. The method of calculating | requiring the generation frequency of the bubble contained in a spiral flow injection molded object by the method of Claim 3 about a spiral flow injection molded object.

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