JP2012233182A - Polypropylene-based resin expanded particle, and polypropylene-based resin in-mold expansion molded product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide polypropylene-based resin expanded particles which allow, in the in-mold expansion molding, significant reduction in molding pressure and stable production even with a currently widely used molding machine having a withstand pressure specification of 0.4 MPa (gauge pressure), and can provide an in-mold expansion molded product having high rigidity and high surface beauty; and in particular, to provide polypropylene-based resin expanded particles capable of providing an in-mold expansion molded product in which a "part which is hard to weld", and/or a thick part and a thin part are mixed, wherein both the weldability of the thick part and the surface beauty of the thin part are achieved.SOLUTION: The polypropylene-based resin expanded particles include, as a base material resin, a polypropylene-based resin which has a specific 1-butene content and a specific ethylene content, and a specific melting point, wherein a DSC curve obtained by the differential scanning calorimetry (DSC) of the polypropylene-based resin expanded particles has two regions of a region of low-temperature-side heat quantity of fusion and a region of high-temperature-side heat quantity of fusion, and the region of low-temperature-side heat quantity of fusion has a maximum value in the differential curve of the DSC curve.

Description

  The present invention relates to polypropylene resin foam particles used for automobile interior members, automobile bumper core materials, heat insulating materials, buffer packaging materials, pass boxes, and the like, and in-mold foam molded articles obtained using the foam particles. is there. In particular, the present invention relates to foamed particles and foamed moldings used in automobile members, passing boxes and the like that require rigidity.

  The in-mold foam molded article obtained using the polypropylene resin foamed particles has characteristics such as shape flexibility, light weight, and heat insulation, which are advantages of the in-mold foam molded article. In-mold foam moldings obtained using polypropylene resin foam particles are more resistant to chemicals, heat and strain after compression compared to in-mold foam moldings obtained using polystyrene resin foam particles. In addition, the dimensional accuracy, heat resistance, and compressive strength are superior as compared with an in-mold foam molded product obtained using polyethylene resin expanded particles.

  Due to these characteristics, in-mold foam molded products obtained using polypropylene resin foam particles are used for various applications such as automotive interior members, automotive bumper core materials, heat insulating materials, shock-absorbing packaging materials, and boxes. ing.

  In particular, in automobile parts and pass boxes that require rigidity, foam particles using a high-rigidity polypropylene-based resin as a base resin are used. Therefore, at the time of in-mold foam molding, 0.4 MPa (gauge pressure) or more The heating steam pressure is required. In general, most of the molding machines for in-mold foam molding of polypropylene resin foamed particles have a pressure resistance specification in which the pressure of heated steam is 0.4 MPa (gauge pressure) or less. Usually, the molded heating steam pressure produced is approximately up to about 0.36 MPa (gauge pressure), and development of highly rigid polypropylene resin expanded particles capable of lowering the heating steam pressure has been carried out.

  Polypropylene-based resin-in-mold foam-molded articles often have high-rigidity products such as automobile interior members, automobile bumper cores, and pass boxes. The rigidity of the polypropylene resin in-mold molded product is largely determined by the rigidity of the raw material resin and the expansion ratio, but at present, products with a high density of the in-mold foam molded product, that is, a low expansion ratio are used for these applications. By using it, high rigidity is satisfied. However, the high density impairs the lightness that is originally required for an in-mold foam molded article. Densification is a means that should be avoided if possible, especially because it causes deterioration of fuel consumption of automobiles to be mounted on automobile parts and the like and leads to an increase in the weight of final waste.

Also, when increasing the rigidity of the resin itself, which is another means to achieve high rigidity,
Production conditions in in-mold foam molding become severe, and molding processing costs also increase. In other words, high-rigidity polypropylene-based resin is generally a resin having a low comonomer content and a high melting point. However, as the melting point of the resin increases, the molding heating steam required to obtain a good molded product is used. The pressure tends to increase. For this reason, when polypropylene resin having higher rigidity is used in order to obtain higher rigidity, it is necessary to use a molding machine or mold having a high pressure resistance specification, which increases equipment costs and utility costs. For this reason, the molding processing cost increases.

On the other hand, in recent years, the number of polypropylene resin-in-mold foam molded products whose appearance is regarded as important is increasing. This requirement is often used in applications such as automobile interior parts and pass boxes used in places where the user can see. Polypropylene resin-in-mold foam-molded products have properties such as rigidity, lightness, and heat insulation that are usually required. In addition, a good appearance is required.
Due to the manufacturing method of the polypropylene resin-in-mold foam-molded product, there are gaps between particles and a turtle shell pattern, but many products that emphasize the appearance do not like them. In order to make the gaps between the particles inconspicuous, generally, a method of increasing the heating steam pressure at the time of in-mold foam molding and promoting fusion between the particles is taken.

  In addition, in order to erase the turtle shell pattern of particles, a technique (for example, refer to Patent Document 1) using a mold in which a fine uneven pattern is transferred to the mold surface is also performed. The heating steam pressure at the time of in-mold foam molding is increased, and the transfer of the uneven pattern to the foam molded body is promoted. As can be seen from these techniques, in order to obtain an in-mold foam molded article with a good appearance with no conspicuous gaps between particles, that is, a molded foam molded article with a high surface beauty, molding at the time of in-mold foam molding. The heating steam pressure needs to be higher than the pressure required for fusion between particles. On the other hand, if the molding heating steam pressure at the time of in-mold foam molding is too high, the surface of the polypropylene resin in-mold foam molding will be wrinkled, or so-called sink marks will be generated and the tortoiseshell pattern will disappear, but the surface There is a problem that the beauty is deteriorated.

In particular, in a highly rigid polypropylene-based resin-molded foam-molded body having parts with different thicknesses, it is necessary to increase the molding heating steam pressure in order to ensure the meltability of the thick part. The pressure becomes too high in the molding of the thin portion, and wrinkles and sink marks are generated in the thin portion and the surface beauty is deteriorated.
On the other hand, if the molding is performed at a low molding heating steam pressure in order to obtain the surface beauty of the thin portion, the meltability of the thick portion is lowered.

  As described above, special molding of high-rigidity and highly beautiful polypropylene-based resin-molded in-mold molded products, particularly high-rigidity polypropylene-based resin-molded in-mold molded products having parts with different thicknesses There is a need for a technique that can be stably produced at a lower molding temperature without using a machine.

  Various techniques have been studied with respect to techniques for improving the rigidity of the polypropylene resin in-mold foam-molded body. In order to obtain high rigidity with a polypropylene resin, it is conceivable to simply use homopolypropylene.

For example, Patent Document 2 discloses a homopolypropylene resin expanded particle having a tensile elastic modulus of 15,000 to 25000 kg / cm ² and a DSC curve obtained by a differential scanning calorimeter having a high-temperature peak heat of 30 to 60 J / g. The technology regarding is disclosed. Further, Patent Document 2 can produce foamed particles capable of obtaining an in-mold foam-molded product at a relatively low molding temperature using a homopropylene resin having an MFR in the range of 20 to 100 g / 10 min. This technique is disclosed.
However, in the technique described in Patent Document 2, it is described that the pressure of the heating steam at the time of molding necessary for obtaining a good foamed molded article is 0.4 to 0.6 MPa (gauge pressure). Thus, it cannot be molded by a molding machine having a 0.4 MPa (gauge pressure) pressure resistance specification. In addition, Patent Document 2 does not particularly describe the surface beauty of the molded body.

Patent Document 3 discloses that the water vapor pressure at the time of in-mold molding is reduced to 0 by using polypropylene-based resin expanded particles of a random copolymer having a homopropylene or α-olefin content of less than 1% by weight. Technical trees that can be reduced to 4 MPa (gauge pressure) or less are disclosed.
However, in the technique described in Patent Document 3, homopolypropylene or a random polypropylene resin having a low comonomer content is used, but there is no particular description regarding the surface beauty.

  As a similar evaluation standard, the evaluation is based on the standard that the fusion between the foamed particles is 60% or more, but the standard is an evaluation standard in which the particles inside the in-mold foam molded product are partially fused, Compared to the standard for obtaining surface aesthetics, this is a standard that can be satisfied even with a low molding heating steam pressure. With the technique described in the publication, it seems that it is difficult to obtain a molded article having a beautiful surface with a molding machine that actually uses 0.4 MPa (gauge pressure) pressure resistance.

  Although high rigidity cannot be obtained as compared with homopolypropylene, a technique using a polypropylene random copolymer has been studied with emphasis on moldability.

  For example, Patent Document 4 discloses a technique using a propylene-based random copolymer having a melting point of 149 to 157 ° C., an MFR of 1 to 20 g / 10 minutes, and a half-crystal time of a certain value or less as a base resin. Has been.

Patent Document 5 discloses a high-temperature side crystal of a melting crystal curve obtained by using differential scanning calorimetry (hereinafter abbreviated as “DSC”) for the crystalline state of polypropylene resin expanded particles used for in-mold foam molding. A technique for improving the compressive strength of the in-mold foam-molded product obtained by setting the relationship between the amount and the low-temperature side crystal amount within a certain range is disclosed.
However, regarding these techniques, the pressure of the heating steam required for in-mold foam molding is as high as 0.4 to 0.5 MPa (gauge pressure), and in particular, the pressure resistance is similar to the techniques described in Patent Documents 2 to 3. This technology is made possible by using a high-performance molding machine.

Furthermore, in Patent Document 6, by using a polypropylene resin containing 1-butene as a comonomer, resin expanded particles having a high tensile elastic modulus, that is, rigidity with respect to the resin melting point are obtained, and by using this, A technique is disclosed in which an in-mold foam molded body having high rigidity can be obtained.
However, with regard to the technique described in Patent Document 6, the pressure of the heating steam necessary for in-mold foam molding is around 0.4 MPa (gauge pressure), which is a relatively low molding heating steam pressure compared to other techniques. Although it is, the lowest one of the examples being implemented is 0.36 MPa (gauge pressure), which is a level just below the specifications of a molding machine of 0.4 MPa (gauge pressure) pressure resistance specification that is often used at present. . Moreover, there is no special description regarding the surface beauty.

Furthermore, Patent Document 7 discloses a polypropylene having high rigidity by using polypropylene-based resin expanded particles whose base resin is a propylene / 1-butene random copolymer containing 3 to 12% by weight of 1-butene component. A technique for obtaining a resin-based foamed molded article is disclosed. When the technique described in Patent Document 7 is used, it is described that molding can be performed even with a molding machine having a pressure resistance of 0.4 MPa (gauge pressure), which is often used at present, and a pressure of molding heating steam around 0.3 MPa (gauge pressure). ing.
However, when the Example of patent document 7 is seen, the rigidity of the in-mold foaming molding obtained with the shaping | molding heating steam pressure of about 0.3 MPa (gauge pressure) is the compression measured at 20 degreeC according to JISK6767. The compressive strength at a strain of 50% is 6.2 kg / cm ² , which is not sufficient for applications requiring high rigidity.

  Further, a 1-butene homopolypropylene resin random copolymer containing no ethylene component has a harder and more brittle property than a polypropylene resin random copolymer containing an ethylene component, and this property is a base material of a foam. When it is used as a resin, it has properties that are poor in dimensional recovery after compression and impact properties in a low temperature region. Polypropylene resin foam molded products are superior to polystyrene resin foam molded products, which are the same in-mold foam molded products, in terms of rigidity, but have superior resistance to repeated impacts and flexibility. Some aspects are used for such purposes. For this reason, the technique described in Patent Document 7 also has a drawback that it is not suitable for general buffer packaging applications other than applications intended only for rigidity.

  As described above, there is a current situation in which special molding machines that can withstand high molding heating steam pressure are used in applications that require high rigidity. However, in order to increase the pressure resistance of the molding machine, it is necessary to increase the size of the machine in order to increase the strength of the molding machine, and it is also necessary to increase the thickness of the mold. There is.

  In addition, increasing the pressure of the molding heating steam increases the amount of steam necessary for heating during molding, which increases the utility cost, for example, increasing the amount of cooling water for cooling this. Furthermore, the heating time at the time of molding becomes longer in order to heat to a higher temperature, and more time is required for the process of cooling the heated mold with cooling water, so the production cycle per product becomes longer. Productivity deteriorates. Furthermore, since the mold shape is complicated in in-mold foam molding, depending on the shape, stress may concentrate on a part of the mold during molding heating, and the mold may be damaged. Become.

  As described above, the high molding heating steam pressure in the in-mold foam molding has various drawbacks, and it is desirable that molding can be performed with the lowest possible molding heating steam pressure. In the category of existing technology, it is difficult to obtain polypropylene-based resin foam particles for in-mold foam molding with high rigidity that can be stably produced with a molding machine with 0.4 MPa (gauge pressure) pressure resistance specifications that are widely used at present. It is. Furthermore, it must be said that there is no present state of the technology that satisfies the surface beauty of the in-mold foam molded article.

  In addition, a technique for imparting new characteristics to a resin by using a mixture of resins having different physical properties has been developed.

  Patent Document 8 includes a resin in which 90 to 10% by weight of a polypropylene resin of MFR 6 to 10 g / 10 min and 10 to 90% by weight of a polypropylene resin MFR 0.5 to 3 g / 10 min are mixed, and the MFR of the mixed resin. Polypropylene-based resin expanded particles, characterized in that is 2 to 5 g / 10 min. It is described that when the foamed particles are used, it is possible to obtain a molded product having good surface properties and fusion of the molded product, no sink marks on the molded product, and a short molding time. However, the gazette mainly shows the effect on the molding time, and does not particularly mention the rigidity. Furthermore, although the publication has an evaluation from the viewpoint of sink marks of the molded article, there is no particular description regarding the surface beauty.

Patent Document 9 discloses polypropylene-based resin expanded particles having an ethylene-propylene-butene random copolymer having a specific melt flow rate, melting point, and flexural modulus as a base resin. Also described is a two-stage expanded particle obtained by a two-stage expansion method in which an internal pressure is applied to the container and then heated with steam. It is described that such two-stage expanded particles can be molded with a low heating vapor pressure.
However, in the technique of Patent Document 9, since the melting point of the base resin is 145 ° C. or less, it is difficult to apply to applications that require rigidity. In addition, when such a two-stage expanded particle is formed into a polypropylene resin-in-mold foam-molded body having portions with different thicknesses, the fusion property of the thick part becomes good, and the surface beauty of the thin part is also improved. There is no mention of superiority.

JP 2000-108134 A JP-A-8-277340 Japanese Patent Laid-Open No. 10-45938 Japanese Patent Laid-Open No. 10-316791 JP-A-11-156879 JP 7-258455 A JP-A-1-242638 JP 2000-327825 A JP 2009-280783 A

  The present invention can greatly reduce the molding pressure in in-mold foam molding of polypropylene-based resin foam particles having high rigidity, and is stable even in a molding machine with a 0.4 MPa (gauge pressure) pressure resistance specification that is widely used at present. It is possible to provide polypropylene-based resin foamed particles that can be produced in a mold, have high rigidity, are excellent in fusion within the in-mold foam-molded body, and have a high surface beauty.

  As a result of diligent research in view of the above problems, the present inventor has found that a low temperature side melting peak (melting calorie region) and a high temperature side melting peak (DSC curve) obtained by differential scanning calorimetry (DSC) of polypropylene resin expanded particles (high temperature side melting peak) Polypropylene resin foam particles having two melting peaks (melting calorie region) in the melting calorie region and having a maximum value in the differential curve of the DSC curve at the low-temperature side melting peak (melting calorie region) Then, by performing in-mold foam molding, it was found that the above problems were solved, and the present invention was completed.

That is, the present invention has the following configuration.
[1] As a comonomer copolymerized with propylene, it contains 1-butene and ethylene, the sum of 1-butene content and ethylene content is 1.0 wt% or more, and 1-butene content is 6.0 wt% or less The polypropylene resin expanded particles having a base resin of a polypropylene resin having an ethylene content of 3.0% by weight or less and a melting point of 140 ° C. or higher and 155 ° C. or lower,
The expansion ratio is 20 times or more and 60 times or less,
In a DSC curve obtained by differential scanning calorimetry (DSC) in which the temperature is raised from 40 ° C. to 220 ° C. at a rate of temperature increase of 10 ° C./minute, the low temperature side melting calorie region (Ql) and the high temperature side melting calorie region (Qh) Have two areas,
The differential in which the ratio (Qh / (Ql + Qh) × 100) (%) of the high temperature side heat of fusion is 10% or more and 30% or less and the temperature is increased from 40 ° C. to 220 ° C. at a temperature increase rate of 20 ° C./min. Polypropylene resin foamed particles having a maximum value between 105 ° C. and 120 ° C. in a differential curve of a DSC curve obtained by scanning calorimetry (DSC).
[2] The polypropylene resin expanded particles according to [1], wherein the polypropylene resin as the base resin has a melting point of 147 ° C. or higher and 153 ° C. or lower.
[3] The polypropylene resin foamed particles according to [1] or [2], which are obtained through at least two foaming steps.
[4] A polypropylene resin-in-mold foam-molded article obtained by foam-molding the polypropylene-based resin foam particles according to any one of [1] to [3].
[5] In an in-mold foam-molded product obtained using a fixed mold and a movable mold, when a polypropylene resin expanded particle is filled in a mold, the shape is formed only by one of the molds. The polypropylene resin-in-mold foam-molded article according to [4], characterized by comprising:
[6] In an in-mold foam molded product obtained using a fixed mold and a movable mold, when a polypropylene resin foam particle is filled in a mold, a part is formed by only one of the molds. The polypropylene resin in-mold foam-molded article according to [5], wherein when the largest sphere is cut out from the part, a sphere having a diameter of 20 mm or more and 100 mm or less can be cut out.
[7] A polypropylene resin-in-mold foam-molded article comprising a bottom surface and a bottom peripheral edge standing wall portion and having an interior capable of storing articles,
Having at least one standing wall on the inner bottom surface;
The thickness of the internal bottom standing wall is 1.2 times or more and 5 times or less the bottom peripheral edge standing wall thickness,
The polypropylene resin-in-mold foam-molded article according to [5] or [6], wherein the height of the internal bottom standing wall portion is not less than 2 times and not more than 30 times the thickness of the bottom surface.
[8] The polypropylene resin-in-mold foam-molded molded product according to [7], wherein the standing wall portion on the inner bottom surface is a standing wall portion for partitioning an interior in which articles can be stored.
[9] The foaming in the polypropylene resin mold according to [7] or [8], wherein a transfer mark at the tip of the filling machine remains on an extension line in the height direction of the standing wall portion on the inner bottom surface. Molded body.
[10] The polypropylene resin-in-mold foam-molded product according to any one of [7] to [9], wherein the polypropylene-based resin mold-in-mold foam-molded product is a luggage box.

  By using the polypropylene resin foamed particles of the present invention for in-mold foam molding, the molding pressure can be greatly reduced. Even with a molding machine with a 0.4 MPa (gauge pressure) pressure resistance specification, which is currently widely used, An in-mold foam-molded article that can be stably produced, has high rigidity, is excellent in fusion within the in-mold foam-molded body, and has excellent surface beauty can be obtained. In particular, in an in-mold foam molded article in which a thick part and a thin part are mixed, an in-mold foam molded article having good fusion properties inside the thick part and good surface beauty of the thin part is obtained. Is possible.

An example of a DSC curve (temperature vs. endothermic amount) obtained from differential scanning calorimetry (DSC) in which the temperature of the polypropylene resin expanded particle of the present invention is increased from 40 ° C. to 220 ° C. at a rate of temperature increase of 10 ° C./min. is there. The DSC curve has two regions of heat of fusion, a low temperature side heat of fusion region and a high temperature side heat of fusion region. Differential curve of DSC curve (differential amount of temperature vs. endotherm) obtained from differential scanning calorimetry (DSC) of polypropylene-based resin expanded particles heated from 40 ° C. to 220 ° C. at a rate of temperature increase of 20 ° C./min. It is an example. In the curve A related to the expanded polypropylene resin particles of the present invention, there is a maximum value (point E) in the range of 105 ° C. or more and 120 ° C. or less, and in the curve B related to the conventional expanded polypropylene resin particles, there is no maximum value. . In order to determine the melting point of the polypropylene resin, in differential scanning calorimetry (DSC), the temperature was increased from 40 ° C. to 220 ° C. at a temperature increase rate of 10 ° C./min, and the temperature was 220 ° C. at a temperature decrease rate of 10 ° C./min. It is an example of the DSC curve at the time of the 2nd temperature increase which performed operation of temperature increase from 40 degreeC to 220 degreeC at the temperature increase rate of 10 degreeC / min. It is a polypropylene-based resin-molded foam-molded body in which a thick part and a thin part used in Examples and Comparative Examples of the present application are mixed, specifically, a box type in which a standing wall part is provided on the inner bottom surface of the box type This is an in-mold foam molded article. In the in-mold foam molding process of the polypropylene resin in-mold foam illustrated in FIG. 4, the polypropylene resin foam particles (lattice part) are passed through a filling machine and the fixed mold (shown as a right-upward slanted part) and the movable mold (down-right). It is an example which shows the cross section at the time of filling the metal mold | die consisting of a hatched part (however, the in-mold foam molding machine which mounts a metal mold | die is not shown in figure). It is an example which expanded the principal part of FIG. 5, and showed the flow of the water vapor | steam at the time of in-mold foam molding.

  In the expanded polypropylene resin particles of the present invention, a DSC curve obtained when differential scanning calorimetry (DSC) is performed at a temperature rising rate of 10 ° C./min from 40 ° C. to 220 ° C. is shown in FIG. As described above, the total heat of fusion is divided into two heat of fusion regions, a low temperature side heat of fusion region and a high temperature side heat of fusion region.

In the present invention, total heat of fusion (Q), low temperature side heat of fusion (Ql), and high temperature side heat of fusion (Qh) are defined as follows.
The total heat of fusion (Q), which is the sum of the low-temperature side heat of fusion (Ql) and the high-temperature side heat of fusion (Qh), is the endotherm at a temperature of 100 ° C. at which the low-temperature side heat of fusion starts in the obtained DSC curve. A line segment AB connecting the endothermic amount (point B) at the temperature at which the high temperature side melting ends is drawn from A), and is a part surrounded by the line segment AB and the DSC curve.
The point at which the endotherm between the two melting calorie regions of the low temperature side melting calorie and the high temperature side calorie of the DSC curve becomes the smallest is point C, and the point that intersects perpendicularly from the point C to the line segment AB is D. The part surrounded by line segment AD, line segment CD, and DSC curve is the low temperature side heat of fusion (Ql), and the part surrounded by line segment BD, line segment CD, and DSC curve is the high temperature side heat of fusion ( Qh).

In the polypropylene resin expanded particles of the present invention, the value of the ratio of the high temperature side heat of fusion (Qh) [= Qh / (Ql + Qh) × 100 (%)] (hereinafter sometimes referred to as “high temperature heat quantity ratio”) It is 10% or more and 30% or less, more preferably 15% or more and 25% or less, and more preferably 15% or more and 20% or less.
When the high temperature calorie ratio is less than 10%, the compression strength of the molded product obtained by in-mold foam molding tends to be low and the practical strength tends to decrease. When the high temperature heat ratio exceeds 30%, the compression strength of the foam obtained by in-mold foam molding increases, but the foaming force of the polypropylene resin foamed particles is too low, and the entire in-mold foam molded body melts. There is a tendency that a poor molding or a high molding pressure is required for fusing.

The expansion ratio of the expanded polypropylene resin particles of the present invention is 20 times or more and 60 times or less, preferably 30 times or more and 50 times or less.
When the expansion ratio of the polypropylene resin expanded particles is less than 20 times, it becomes difficult to obtain polypropylene resin expanded particles having a minimum value in the differential curve of the DSC curve in the low-temperature side calorie region, and the molding pressure for obtaining the in-mold foam Tend to be higher. On the other hand, when the expansion ratio exceeds 60 times, the practical mechanical properties such as the compression strength of the polypropylene resin in-mold foam molded product obtained by in-mold foam molding tend to be lowered.

In the present invention, the expansion ratio of the expanded polypropylene resin particles means that after measuring the weight w (g) of the expanded polypropylene resin particles, the volume v (cm ³ ) is measured by a submersion method, and expanded polypropylene resin foam. The true specific gravity ρb = w / v of the particles is obtained, and is the ratio (ρr / ρb) to the density ρr (0.9 g / cm ^{3 in the} present application) of the polypropylene resin particles before foaming.

  In the expanded polypropylene resin particles of the present invention, the most important point is the differential curve of the DSC curve obtained by differential scanning calorimetry (DSC) in which the temperature is raised from 40 ° C. to 220 ° C. at a rate of temperature increase of 20 ° C./min. The maximum value between 105 ° C. and 120 ° C.

  As shown in FIG. 2, the differential curve of the DSC curve of the polypropylene resin expanded particles in the present invention has a maximum value (point E) in the low-temperature side melting heat amount region. The maximum value (point E) indicates the heat history temperature applied to the polypropylene resin particles and greatly affects the molding pressure for obtaining the molded product in the mold, and the temperature indicating the maximum value of the differential curve is 105 ° C. or higher and 120 ° C. The temperature is preferably 110 ° C. or higher and more preferably 110 ° C. or higher and 115 ° C. or lower.

  When the temperature showing the maximum value in the differential curve is less than 105 ° C., the resulting polypropylene resin in-mold foam molded product tends to be poorly fused or requires a high molding pressure to be fused. . On the other hand, when the temperature showing the maximum value exceeds 120 ° C., the cell membrane in the polypropylene resin expanded particles breaks down, the resulting molded product has a large shrinkage rate, generates large wrinkles, and obtains a good molded product. There is a tendency to not be able to.

In the low temperature side melting calorie | heat amount area | region in this invention, the polypropylene resin expanded particle which has the maximum value in the differential curve of a DSC curve can be easily obtained by combining the following methods, for example.
(1) After obtaining expanded polypropylene resin particles, after impregnating with an inorganic gas (for example, air, nitrogen, carbon dioxide, etc.) and applying an internal pressure, at least contact with water vapor at a specific pressure. A method through two foaming steps,
(2) 0.05 or more of at least one hydrophilic compound selected from the group consisting of glycerin, polyethylene glycol, a glycerin ester of a fatty acid having 10 to 25 carbon atoms, or a water-absorbing substance such as melamine and isoanuric acid. A method of foaming polypropylene-based resin particles comprising 2% by weight to 2% by weight in heated steam;
(3) A method of foaming into heated steam using, as a raw material, polypropylene resin particles obtained by blending a plurality of polypropylene resins can be mentioned.

The polypropylene resin as the base resin of the expanded polypropylene resin particles of the present invention is a copolymer resin containing 1-butene and ethylene as propylene as a comonomer.
However, it may contain a comonomer other than 1-butene and ethylene. Examples of the copolymerizable comonomer include isobutene, 1-pentene, 3-methyl-1-butene, 1-hexene, 4-methyl- 1-pentene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-decene and other α-olefins having 2 or 4 to 12 carbon atoms, cyclopentene, norbornene Cyclic olefins such as tetracyclo [6,2,11,8,13,6] -4-dodecene, 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 1,4-hexadiene, methyl-1, Dienes such as 4-hexadiene and 7-methyl-1,6-octadiene, vinyl chloride, vinylidene chloride, acrylonitrile, vinyl acetate , Acrylic acid, methacrylic acid, maleic acid, ethyl acrylate, butyl acrylate, methyl methacrylate, maleic anhydride, styrene, methyl styrene, vinyl toluene, and vinyl monomers such as divinylbenzene.
These may be used alone or in combination.

  However, it is preferable to use only 1-butene and ethylene as a comonomer from the viewpoint of excellent foamability when obtaining polypropylene resin foamed particles and excellent surface beauty when formed into a polypropylene resin mold. .

  The base resin used for the expanded polypropylene resin particles of the present invention includes at least 1-butene and ethylene as a comonomer, and the total 1-butene content and ethylene content is 1.0% by weight or more, and A polypropylene resin having a 1-butene content of 6.0% by weight or less, an ethylene content of 3.0% by weight or less, and a melting point of 140 ° C. or more and 155 ° C. or less.

  A polypropylene resin having a sum of 1-butene content and ethylene content of less than 1% by weight is a resin having a melting point exceeding 160 ° C. Even when the obtained expanded particles are subjected to in-mold foam molding, the molding pressure is 0. The pressure may exceed 40 MPa (gauge pressure), and molding may be difficult. In addition, even if the foamed particles obtained are subjected to in-mold foam molding at a molding pressure of 0.40 MPa (gauge pressure) or less, the appearance of the resulting molded product tends to be significantly impaired.

  The 1-butene content in the base resin used for the expanded polypropylene resin particles of the present invention is 6.0% by weight or less, more preferably 3.0% by weight or more and 5.0% by weight or less. When the 1-butene content exceeds 6.0% by weight, the melting point of the base resin becomes less than 140 ° C., and the steam heating pressure at the time of in-mold foam molding is reduced, but the rigidity of the polypropylene resin itself becomes weak and practical. There is a tendency not to satisfy rigidity.

The ethylene content in the base resin used in the polypropylene resin expanded particles of the present invention is 3.0% by weight or less, preferably 1.0% by weight or less, and 0.2% by weight or more and 1.0% by weight. The following is more preferable.
When the ethylene content exceeds 3.0% by weight, the rigidity (compression strength) of the foamed molded product tends to be low, and there is a tendency that it cannot withstand the practical rigidity of automobile members and the like.
Further, the melting point of the base resin is preferably 146 ° C. or higher and 154 ° C. or lower, and most preferably 147 ° C. or higher and 153 ° C. or lower from the viewpoint of achieving a low molding pressure while ensuring high rigidity.

  The polypropylene resin having a specific 1-butene content or ethylene content and having a specific melting point as described above can be selected based on a catalog or information of a polypropylene resin manufacturer, and a polypropylene resin manufacturer. Can be produced by a known technique.

  The polypropylene resin as the base resin used in the present invention is preferably in an uncrosslinked state, but may be crosslinked with an organic peroxide or radiation.

  Polypropylene resin as a base resin used in the present invention is made of other thermoplastic resins that can be mixed with polypropylene resin, such as low density polyethylene, linear density polyethylene, polystyrene, polybutene, ionomer, etc. Mixtures may be used as long as the characteristics of the resin are not lost.

  The polypropylene resin as a base resin used in the present invention is a hydrophilic compound that promotes improvement of the expansion ratio to the extent that the properties of the polypropylene resin are not impaired, a foam nucleating agent that promotes the formation of cell nuclei during foaming, and a compatibilizing agent. Further, an antistatic agent, a colorant, and the like can be added.

  Hydrophilic compounds that promote the improvement of the expansion ratio include water-absorbing organic substances such as glycerin, polyethylene glycol, glycerin fatty acid ester, melamine, isocyanuric acid, melamine / isocyanuric acid condensate, sodium chloride, calcium chloride, magnesium chloride, borax, and boron. Examples thereof include water-soluble inorganic substances such as calcium acid and zinc borate, and fatty alcohols having 12 to 18 carbon atoms such as cetyl alcohol and stearyl alcohol.

  Foam nucleating agents that promote the formation of cell nuclei during foaming include talc, calcium carbonate, silica, kaolin, barium sulfate, calcium hydroxide, aluminum hydroxide, aluminum oxide, titanium oxide, zeolite and other inorganic substances, calcium stearate, stearin Examples include fatty acid metal salts such as barium acid.

In producing the polypropylene resin expanded particles of the present invention, first, polypropylene resin particles are produced.
Examples of the method for producing polypropylene resin particles include a method using an extruder.
Specifically, for example, a polypropylene compound is previously blended with a hydrophilic compound, a foam nucleating agent, and other additives as necessary, and the blend is put into an extruder, melt-kneaded, and extruded from a die. After cooling, it can be made into a particle shape by chopping with a cutter.

  The polypropylene resin particles of the present invention can be produced using the polypropylene resin particles obtained as described above.

As a preferred embodiment for producing the polypropylene resin expanded particles of the present invention,
In a closed container, polypropylene resin particles are dispersed in an aqueous dispersion medium together with a foaming agent such as carbon dioxide, heated and pressurized to a temperature equal to or higher than the softening temperature of the polypropylene resin particles, and then a pressure lower than the internal pressure of the sealed container. There is a method for producing polypropylene resin foamed particles in an aqueous dispersion, which is obtained through a foaming step that is released into the region.

In particular,
(1) After charging polypropylene resin particles and an aqueous dispersion medium, a dispersing agent, etc., if necessary, the inside of the sealed container is evacuated and then 1 MPa (gauge pressure) or more. A foaming agent of 2 MPa or less (gauge pressure) is introduced and heated to a temperature equal to or higher than the softening temperature of the polypropylene resin. By heating, the pressure in the sealed container rises to about 2 MPa (gauge pressure) or more and 5 MPa or less (gauge pressure). If necessary, add a foaming agent near the foaming temperature to adjust to the desired foaming pressure, adjust the temperature further, and then release it to a pressure range lower than the internal pressure of the sealed container. Resin foam particles can be obtained.

As another preferred embodiment,
(2) After charging polypropylene-based resin particles, aqueous dispersion medium, and dispersing agent, if necessary, into a sealed container, evacuating the sealed container as necessary, until the temperature is equal to or higher than the softening temperature of the polypropylene-based resin A foaming agent may be introduced while heating.

Furthermore, as another preferred embodiment,
(3) After charging polypropylene-based resin particles, aqueous dispersion medium, and dispersing agent if necessary into a sealed container, heat to near the foaming temperature, introduce a foaming agent, set the foaming temperature, and from the internal pressure of the sealed container Further, it is possible to obtain expanded polypropylene resin particles by releasing into a low pressure range.

  Before releasing into the low pressure region, carbon dioxide, nitrogen, air or a substance used as a foaming agent is injected to increase the internal pressure in the sealed container, and the pressure release speed during foaming is adjusted. The foaming ratio can be adjusted by controlling the pressure by introducing carbon dioxide, nitrogen, air, or a substance used as a foaming agent into the sealed container even during release to the low pressure region.

  In the DSC curve obtained by differential scanning calorimetry (DSC) in which the polypropylene resin expanded particles of the present invention are heated at a temperature rising rate of 10 ° C./min as described above, Has two heats of fusion.

  Polypropylene resin foamed particles having two heat of calorie regions can be easily obtained by setting the temperature in the sealed container to an appropriate value during foaming in the above-described method for producing polypropylene resin foamed particles in an aqueous dispersion. can get.

  That is, as the temperature in the sealed container at the time of foaming, when the melting point of the polypropylene resin as the base resin is Tm and the melting end temperature is Tf, it is preferably Tm-10 (° C.) or higher, and Tm-8 ( More preferably, the temperature is Tm-5 (° C.) or more and Tf-2 (° C.) or less.

Here, as shown in FIG. 3, the melting point Tm of the polypropylene resin is a rate of 10 ° C./min from 40 ° C. to 220 ° C. of 1 mg to 10 mg of polypropylene resin using a differential scanning calorimeter DSC. In the DSC curve obtained when the temperature was raised from 220 ° C. to 40 ° C. at a rate of 10 ° C./min and then raised again from 40 ° C. to 220 ° C. at a rate of 10 ° C./min. It is the melting peak temperature when warm.
The melting end temperature Tf is a temperature at which the high temperature side tail of the melting peak at the second temperature increase returns to the baseline position on the high temperature side.

  For example, the ratio [= Qh / (Ql + Qh) × 100 (%)] of the high temperature side heat of fusion (Qh) described above is the holding time at the temperature in the closed container (after reaching the desired temperature in the closed container, foaming is performed. Holding time), foaming temperature (temperature at the time of foaming, which may be the same as or different from the temperature in the closed container), foaming pressure (pressure at the time of foaming), etc. . In general, the DSC ratio or the high temperature side melting peak heat amount tends to increase by increasing the holding time, lowering the foaming temperature, or lowering the foaming pressure. From the above, it is possible to easily find a condition that provides a desired high-temperature side heat of fusion ratio by performing several experiments in which the holding time, foaming temperature, and foaming pressure are systematically changed as appropriate. The foaming pressure can be adjusted by adjusting the amount of foaming agent.

  In the present invention, the sealed container in which the polypropylene resin particles are dispersed is not particularly limited as long as it can withstand the pressure in the container and the temperature in the container at the time of producing the foamed particles. For example, an autoclave pressure container Is given.

  Examples of the blowing agent used in the present invention include saturated hydrocarbons such as propane, butane and pentane, ethers such as dimethyl ether, alcohols such as methanol and ethanol, inorganic gases such as air, nitrogen, carbon dioxide and water. Is mentioned. Among these, it is desirable to use carbon dioxide or water because it has a particularly low environmental load and no danger of combustion.

In the present invention, it is preferable to use a dispersant and a dispersion aid in order to prevent coalescence of polyethylene resin particles in the aqueous dispersion medium.
Examples of the dispersant include inorganic dispersants such as tricalcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, and clay. These may be used alone or in combination of two or more.

  Dispersion aids include carboxylic acid salt types, alkyl sulfonates, n-paraffin sulfonates, alkyl benzene sulfonates, alkyl naphthalene sulfonates, sulfosuccinates, sulfonates, sulfated oils, alkyl sulfates And anionic surfactants such as sulfates such as alkyl ether sulfates and alkylamide sulfates, and phosphates such as alkyl phosphates, polyoxyethylene phosphates, and alkyl allyl ether sulfates. it can. These may be used alone or in combination of two or more.

  Among these, it is preferable to use at least one selected from the group consisting of tricalcium phosphate, tribasic magnesium phosphate, barium sulfate or kaolin as a dispersant and n-paraffin sulfonic acid soda as a dispersion aid.

  In the present invention, the polypropylene resin particles are usually used in an amount of 20 to 100 parts by weight with respect to 100 parts by weight of the aqueous dispersion medium in order to improve the dispersibility in the aqueous dispersion medium. Is preferred.

  In addition to the above-described method for producing polypropylene resin foamed particles in an aqueous dispersion system, without using an aqueous dispersion medium, for example, by directly contacting the foaming agent with the polypropylene resin particles in a closed container, It is also possible to obtain expandable polypropylene resin particles by impregnating the expandable polypropylene resin particles and then expanding the expandable polypropylene resin particles by bringing water vapor into contact with the expandable polypropylene resin particles.

  As described above, the process of obtaining the polypropylene resin expanded particles from the polypropylene resin particles is sometimes referred to as “one-stage expanded process”, and the polypropylene resin expanded particles obtained in this way are referred to as “one-stage expanded particles”. There is.

Depending on the type of foaming agent used in the production of the first-stage expanded particles, the expansion ratio may not reach 10 times. Furthermore, in the differential curve of the DSC curve of the heating rate of 20 ° C./min of the single-stage expanded particles, the maximum value of the differential curve may not appear at 105 ° C. or higher and 120 ° C. or lower.
In such a case, the single-stage foamed particles are impregnated with an inorganic gas (for example, air, nitrogen, carbon dioxide, etc.) and given an internal pressure, and then contacted with water vapor at a specific pressure, whereby the single-stage foam particles are obtained. The expanded polypropylene resin particles of the present invention having a maximum value at 105 ° C. or more and 120 ° C. or less in the differential curve of the DSC curve at a heating rate of 20 ° C./min. Can be obtained.

  As described above, the process of further expanding the polypropylene resin expanded particles to obtain a polypropylene resin expanded particle having a higher expansion ratio may be referred to as a “two-stage expansion process”. By passing through the two-stage foaming step, the foamed particles of the present invention having a maximum value can be obtained in the DSC differential curve in the low temperature side calorific value region of 105 ° C. or more and 120 ° C. or less. Polypropylene resin foam particles obtained through such a two-stage foaming process may be referred to as “two-stage foam particles”.

  In the present invention, when the pressure of water vapor in the two-stage foaming step is to obtain two-stage foamed particles having a maximum value at 105 ° C. or more and 120 ° C. or less in the differential curve of the DSC curve at a temperature increase rate of 20 ° C./min. It is very important, and it is preferable to adjust to 0.04 MPa (gauge pressure) or more and 0.25 MPa (gauge pressure) or less, considering the expansion ratio of the two-stage expanded particles, 0.05 MPa (gauge pressure) or more More preferably, it is adjusted to 0.15 MPa (gauge pressure) or less.

  If the water vapor pressure in the two-stage foaming process is less than 0.04 MPa (gauge pressure), the maximum value may not be expressed in the differential curve, and if it exceeds 0.25 MPa (gauge pressure), the maximum value in the differential curve is Although it develops, the resulting two-stage foam particles tend to coalesce and block, and cannot be used for subsequent in-mold foam molding.

  The internal pressure of the air impregnated in the first-stage expanded particles is preferably changed in consideration of the expansion ratio of the second-stage expanded particles and the water vapor pressure in the second-stage expansion process, but is 0.2 MPa or more (absolute pressure) 0.6 MPa or less (Absolute pressure) is preferred.

  If the internal pressure of the air impregnated in the first-stage expanded particles is less than 0.2 MPa (absolute pressure), high-pressure steam is required to improve the expansion ratio, and the second-stage expanded particles tend to block. When the internal pressure of the air impregnated in the first-stage expanded particles exceeds 0.6 MPa (absolute pressure), the water vapor pressure for obtaining the desired expansion ratio becomes lower, and the second-stage expanded particles having no maximum value in the differential curve Tend to be.

  Thus, compared with the one-stage foaming process, the polypropylene resin foamed particles obtained through two or more foaming processes as in the two-stage foaming process have a differential curve of the DSC curve with a temperature rising rate of 20 ° C./min. , A maximum value between 105 ° C. and 120 ° C. is preferable in the present invention.

  The polypropylene resin expanded particles of the present invention obtained as described above have a feature that the passage of water vapor during in-mold foam molding is better than conventional polypropylene resin expanded particles.

In the conventional polypropylene resin expanded particles, in the in-mold foam molding, when water vapor is ejected from the mold surface, only the polypropylene resin expanded particles in the vicinity of the mold surface are rapidly expanded and fused, Since it becomes difficult for water vapor to pass through the portion corresponding to the inside of the in-mold foam molded body, the temperature in the vicinity of the mold surface rises, but the temperature inside the in-mold foam molded body does not rise. As a result, the surface of the in-mold foam molded body corresponding to the vicinity of the mold surface was beautiful, but the polypropylene resin foam particles inside the in-mold foam molded body were liable to be inferior in adhesion.
And, in order to improve the fusion property inside the in-mold foam molded body, it is necessary to increase the water vapor pressure (increase the water vapor temperature).

In addition, the decrease in the meltability inside the in-mold foam molded product also depends on the shape of the obtained in-mold foam molded product.
For example, in an in-mold foam molded body using a fixed mold and a movable mold, in a shape having a portion where the shape is formed only by either one of the molds, the portion is at the time of in-mold foam molding, Since the passage of water vapor is lower than in other parts, the fusing property tends to decrease.
In addition, “in the in-mold foam-molded article using the fixed mold and the movable mold, when the foam particles are filled in the mold, the portion where only one mold is formed” will be referred to as “ It is abbreviated as “a site difficult to fuse”.

As a specific example of the “parts difficult to fuse”, for example, the internal bottom standing wall portion of FIG. 4 or FIG.
As another in-mold foam-molded product shape in which the fusibility is likely to be lowered, for example, an in-mold foam-molded product in which a thick part and a thin part are mixed can be cited. In the in-mold foam molded product with both thick and thin parts, if the surface aesthetics are prioritized, the meltability inside the thick part is significantly reduced, even if the meltability inside the thin part can be secured. Conversely, if the water vapor pressure is increased with priority given to the fusing property inside the thick part, an excessive water vapor pressure is applied to the thin part, and the partial pressure of air in the foamed particles is reduced. Or wrinkles due to shrinkage, resulting in a decrease in surface aesthetics. That is, there is a tendency that it is difficult to balance the fusion property and the surface beauty.

  For this reason, in particular, in the case where the “fusible part” is a thick part, the problem of a decrease in fusibility becomes remarkable. Furthermore, in an in-mold foam molded product in which the “fusible part” is a thick part and the thin part is in another part, the balance between the meltability and the surface beauty becomes extremely difficult.

  On the other hand, since the polypropylene resin expanded particles of the present invention have good water vapor passage during in-mold foam molding, it becomes possible to ensure the fusion property of the “fusible part”. . In addition, in an in-mold foam molded product in which a thick part and a thin part are mixed, there is no need to perform in-mold foam molding with an excessive water vapor pressure in order to improve the fusing property inside the thick part. It is possible to obtain an in-mold foam-molded article having good fusion properties inside the thick part and good surface beauty of the thin part.

  The polypropylene resin foamed particles of the present invention can be made into a polypropylene resin in-mold foam-molded product by a conventionally known in-mold foam molding method.

As an in-mold foam molding method, for example,
B) After the polypropylene resin foamed particles are pressurized with an inorganic gas such as air, nitrogen, carbon dioxide and the like, the polypropylene resin foamed particles are impregnated with the inorganic gas and given a predetermined polypropylene resin foamed particle internal pressure, A method of filling a mold and heat-sealing with steam,
B) A method in which polypropylene resin foamed particles are compressed with gas pressure and filled in a mold, and heat recovery is performed with water vapor using the recovery force of the polypropylene resin foamed particles.
C) A method such as a method in which a polypropylene resin expanded particle is filled in a mold without heat treatment and heat-sealed with water vapor can be used.

  There is no restriction | limiting in particular in the polypropylene resin in-mold expansion molding obtained from the polypropylene resin expanded particle of this invention. However, from the viewpoint of the remarkable feature that the water vapor passage is good when the in-mold foam molding of the polypropylene resin foamed particles of the present invention is performed, as described above, the polypropylene resin in-mold foam-molded article, It can be suitably used for a polypropylene-based resin mold internal foam having a “part where fusion is difficult” and / or a polypropylene-based resin mold internal foam molded body in which a thick part and a thin part are mixed.

  As a specific example of a polypropylene resin mold foam having a “fusible part” and / or a polypropylene resin mold foam molding in which a thick part and a thin part are mixed, for example, FIG. As shown in the drawing, there can be mentioned a polypropylene-based resin-mold-in-mold foam-molded article having a bottom and a bottom-periphery standing wall portion, having an interior capable of storing articles, and having at least one standing wall portion on the inner bottom surface.

As described above, the inner bottom standing wall portion in FIG. 4 is a “fusible part” that can be formed with only one mold (see also FIG. 5). In FIG. 4, both ends of the inner bottom standing wall are fused and joined to the bottom peripheral standing wall, but only one of them is fused and joined, and the other may be spaced apart from the bottom peripheral standing wall. good. Further, both ends may be separated from the bottom peripheral edge standing wall portion.
On the other hand, the bottom peripheral edge standing wall portion in FIG. 4 is not the inside of the bottom surface but the peripheral wall standing wall portion. Unlike the “fusible part”, in-mold foaming using a fixed mold and a movable mold. In the molded body, when foamed particles are filled in a mold, it is a part where a shape can be formed by both molds.

Note that FIG. 4 shows a case where the angle between the inner bottom surface standing wall portion or the bottom peripheral edge standing wall portion and the bottom surface is vertical, but the angle may be vertical or may not be vertical.
The thicknesses of the bottom surface, bottom peripheral edge standing wall portion, and internal bottom surface standing wall portion in FIG. 4 are as shown in FIG.

Each thickness is the shortest distance (hereinafter also simply referred to as “shortest distance”) between a certain point on one surface and the other surface opposite to the one surface on one surface and the other surface. .
A set of two opposing surfaces may or may not be parallel. The “surface” here may be a flat surface or a curved surface.
The “shortest distance” is a distance from a point on the other surface to a contact point when a perpendicular is extended on the plane when at least one surface is a plane.
On the other hand, when the part shape is circular, approximately circular or elliptical, it is a closed surface and there are actually no two surfaces. However, in the case of circular or approximately circular, the diameter is the shortest distance. The shortest length is the short axis length (minor axis).
Note that the thickness may be constant or not constant in one part.

In FIG. 4, the height of the bottom peripheral edge standing wall portion and the inner bottom standing wall portion is the shortest distance from one point to the bottom surface of the upper end portion of the standing wall portion.
In addition, in one standing wall part, height may be constant and does not need to be constant.
In FIG. 4, the height of the inner bottom surface standing wall portion is the same as the height of the bottom surface peripheral wall portion, but may be different.
Further, the number of internal bottom surface standing wall portions is one in FIG. 4, but may be plural.

As a method for in-mold foam molding of the polypropylene resin in-mold foam molded body shown in FIG. 4, a method comprising the following steps using a mold composed of a fixed mold and a movable mold as shown in FIG. It can be illustrated.
(1) As shown in FIG. > And a moving mold (shown as a downward slanting slanted portion) are filled with polypropylene resin expanded particles (lattice portions) through a filling machine (hereinafter referred to as “filling step”).
(2) Open steam valve A and drain valve A, open steam valve B and drain valve B, and flow steam from steam valves A and B to expel air present in the mold chamber and mold Step of heating the whole (hereinafter referred to as “preheating step”).
(3) Opening the steam valve A and the drain valve B, keeping the steam valve B and the drain valve A closed, and allowing water vapor to flow from the steam valve A, between the polypropylene resin foam particles filled in the mold A process of expelling existing air and heating (hereinafter referred to as “one heating process”).
(4) Next, the steam valve B and the drain valve A are opened, the steam valve A and the drain valve B are closed, and water vapor is allowed to flow from the steam valve B. A process of further expelling air present between them and heating (hereinafter referred to as “reverse one heating process”).
(5) Opening the steam valves A and B, closing the drain valves A and B, and flowing water vapor from the steam valves A and B, until the surface of the polypropylene resin foam particles filled in the mold is softened, A step of raising the temperature sufficiently and finally fusing the polypropylene resin foamed particles to form a polypropylene resin in-mold foam molded product having a fixed shape (hereinafter referred to as “double-side heating step”).
(6) A step of opening the die after cooling the die and taking out the expanded foam in the polypropylene resin mold (hereinafter referred to as “cooling / removing step”).

  By the way, in the one heating process and the reverse one heating process, since a differential pressure is generated between the chamber A and the chamber B, water vapor flows from one chamber to the other chamber. And as for the four directions of the solid line arrow C corresponding to the thickness direction of the bottom-surface periphery standing wall part of FIG. 6, and the solid line arrow D corresponding to the thickness direction of a bottom face, while the said differential pressure exists, Since the thickness is relatively thin (thin wall portion), the passage of water vapor is good, and the temperature rise of the filled polypropylene resin expanded particles occurs rapidly.

  On the other hand, since the two directions of the broken line arrow E corresponding to the thickness direction of the internal bottom standing wall face only the chamber B, there is no chamber differential pressure, so that the passage of water vapor becomes worse and the filling is completed. There is a tendency that the temperature of the expanded polypropylene resin expanded particles is difficult to increase. For this reason, when the thickness of the internal bottom surface standing wall portion is thick, the internal bottom surface standing wall portion tends to be less adhesive than the bottom surface or bottom peripheral edge standing wall portion, and the height of the internal bottom surface standing wall portion is further increased. When the value is large, the flow of water vapor in the portion in the direction of 90 degrees with respect to the broken line arrow E also tends to decrease, and the tendency for the fusion property to decrease further increases.

  However, when the thickness of the internal bottom standing wall is thin, the temperature rise of the filled polypropylene resin foamed particles is secured even by heat transfer from the mold, so from the bottom or bottom peripheral edge standing wall, etc. The problem that the fusing property is lowered is not so remarkable.

  In addition, the molding die is provided with a plurality of steam passages (not shown) called core vents. In a mold shape in which the inner bottom standing wall is formed by a movable mold, it may be difficult to provide a core vent in the mold part that forms the inner bottom standing wall from the viewpoint of workability when providing the core vent. In some cases, it is difficult to provide only a drill hole or the like having a smaller hole diameter than the core vent provided in other portions, and the passage of water vapor tends to be worse.

  Furthermore, as illustrated in FIGS. 5 and 6, when a filling machine is installed on the extension line in the height direction of the internal bottom wall, the core vent can be provided in the fixed part. In addition, the passage of water vapor becomes worse. Furthermore, in this case, since the filling property of the polypropylene resin expanded particles in the internal bottom standing wall portion is good, the filling rate of the polypropylene resin expanded particles in the part tends to be higher than other parts, Water vapor tends to be bad.

  As for the installation position of the filling machine, the shape of the tip part of the filling machine is transferred to the obtained polypropylene-based resin mold foam molding, so the filling machine is installed on the extension line in the height direction of the internal bottom wall standing wall. It can be easily discriminated whether or not it is done.

  For this reason, in order to improve the fusing property of the thick inner bottom standing wall portion, the heating steam pressure at the time of in-mold foam molding must be increased. In that case, the heating water vapor pressure becomes an excessive heating water vapor pressure especially for a thin wall portion such as a bottom peripheral edge standing wall portion. As a result, the surface beauty of the thin wall portion such as the bottom peripheral edge standing wall is lowered, and in the prior art, both the fusion of the thick internal bottom surface standing wall portion and the surface beauty of the thin wall portion are achieved. It was difficult to make.

  On the other hand, the expanded polypropylene resin particles of the present invention have the feature that water vapor can pass better than the expanded polypropylene resin particles of the present invention. Molding can be performed with a heating steam pressure lower than that in the case of molding, and the above-described polypropylene resin in-mold foam-molded article having the “difficult-to-fuse part” can have good fusion properties. In addition, even when the above-mentioned inner bottom standing wall portion is a thick portion, good fusing property is exhibited, and the surface beauty of the thin wall portion such as the bottom peripheral edge standing wall portion and the bottom surface is not impaired, It is possible to achieve both wearability and surface beauty.

In the present invention, there is no particular limitation on the shape of the “parts difficult to fuse”. In the polypropylene resin foamed particles of the present invention, the fusion property is improved and the effect becomes remarkable. From this point of view, the most preferable shape is a shape in which the diameter of the sphere is 30 mm or more and 80 mm or less when the largest sphere is cut out.
If it is a shape that can cut out only a sphere having a diameter of less than 20 mm, the effect of the present invention is not significant with respect to the prior art, and in the case of a shape that can cut out a sphere having a diameter of more than 100 mm, In addition, there is a tendency that it is difficult to perform in-mold foam molding with good fusion properties.

In addition, among the polypropylene-based resin-in-mold foam-molded bodies having the inner bottom standing wall portion and the bottom peripheral edge standing wall portion as described above,
A polypropylene resin-in-mold foam-molded body having an interior capable of storing articles consisting of a bottom surface and a bottom peripheral edge standing wall,
Having at least one standing wall on the inner bottom surface;
The thickness of the standing wall portion of the inner bottom surface is 1.2 times or more and 5 times or less of the bottom peripheral edge standing wall portion thickness,
In polypropylene-type resin-molded in-mold molded products in which the height of the standing wall on the inner bottom surface is 2 to 25 times the thickness of the bottom surface, it is possible to achieve both improved fusion of the thick part and beautiful surface of the thin part. The remarkable effect is expressed. Therefore, it is more preferable to use the polypropylene resin foamed particles of the present invention for molding a polypropylene resin in-mold foam molded product having the shape.
As a more preferable aspect of the shape, the thickness of the standing wall portion of the inner bottom surface is 1.5 times or more and 4 times or less the thickness of the bottom peripheral edge standing wall portion, and the height of the inner bottom surface standing wall portion is 5 times the thickness of the bottom surface. It is not less than 25 times and not more than 25 times.

  However, the thickness of the standing wall portion on the inner bottom surface, the thickness of the bottom wall peripheral standing wall portion, the height of the standing wall portion on the inner bottom surface, and the thickness of the bottom surface do not have to be constant in the in-mold foam molded body. If it is not constant in the in-mold foam molded body, the thickness of the inner bottom wall is the largest thickness of the part, and the bottom peripheral edge standing wall part is the smallest thickness of the part. The above-mentioned ratio is obtained by adopting the largest height of the part as the height of the part and the smallest thickness of the part as the thickness of the bottom part.

  Furthermore, it is more preferable to use the polypropylene resin foamed particles of the present invention in order to obtain a polypropylene resin-in-mold foam-molded product obtained by providing a filling machine on the extension line in the height direction of the inner bottom standing wall portion. It is an aspect.

In addition, the standing wall portion on the inner bottom surface is preferably a standing wall portion for partitioning the inside where the article can be stored. Specifically, the standing wall portion is designed with a luggage box, a tool box, a passing box, or the like. is there.
Among these, in a luggage box having a bottom peripheral edge standing wall portion and a bottom surface having a relatively large area and a thick internal bottom surface standing wall portion, a remarkable effect can be obtained, so that it can be preferably used. That is, the bottom peripheral edge standing wall portion and the bottom surface having a large area in the luggage box are prone to notice sink marks and wrinkles on the surface, but when the polypropylene resin foamed particles of the present invention are used, In addition to excellent fusion of the wall, the bottom peripheral edge standing wall having a large area and the surface beauty of the bottom are also excellent.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to such examples.

In the examples and comparative examples, the substances used were as follows, but no particular purification was performed.
● Polypropylene resin: Polypropylene resin shown in Table 1 [manufactured by Prime Polymer Co., Ltd.]
● Polyethylene glycol: Lion Corporation, average molecular weight 300
● Melamine: Nissan Chemical Co., Ltd. ● Talc: Hayashi Kasei Co., Ltd., Talcan Powder PK-S

  The evaluation in the examples and comparative examples was performed by the following method.

(Quantification of copolymer composition)
Add 50 g of xylene to polypropylene resin (about 1 g), heat and dissolve at 120 ° C., and use high-temperature centrifuge (produced by Kokusan Centrifuge, H175) under the condition of 12000 rpm × 30 minutes, insoluble and soluble components Sorted into After cooling the obtained soluble matter, insoluble matter was obtained by centrifugation (12000 rpm × 30 minutes).
0.4 g of orthodichlorobenzene-d ₄ was added to 50 mg of the obtained insoluble matter, and the mixture was heated and melted at 100 ° C., and measurement was performed at 98 ° C. using ¹³ C-MNR [VARIAN, INOVA AS600]. The copolymer composition of propylene, butene and ethylene was quantified.

(Expansion ratio of expanded particles)
After taking 3 g or more and 10 g or less of the obtained expanded particles, drying at 60 ° C. for 6 hours, adjusting the condition in a room at 23 ° C. and 50% humidity, measuring the weight w (g), and then subtracting the volume v by submerging method. (Cm ³ ) was measured to determine the true specific gravity ρb = w / v of the expanded particles, and the expansion ratio K = ρr / ρb was determined from the ratio to the density ρr of the polypropylene resin particles before expansion.
In the following examples and comparative examples, the density ρr of the polypropylene resin particles before foaming is 0.90 g / cm ³ .

(Measurement of melting point of polypropylene resin)
The melting point was measured by using a differential scanning calorimeter DSC [Seiko Instruments Co., Ltd., DSC6200 type], and obtained polypropylene resin particles 5 to 6 mg at a heating rate of 10 ° C./min from 40 ° C. to 220 ° C. The resin particles are melted by heating to 40 ° C., and then crystallized by cooling from 220 ° C. to 40 ° C. at a temperature lowering rate of 10 ° C./min, and further from 40 ° C. at a temperature rising rate of 10 ° C./min. This is a value obtained as a melting peak temperature at the second temperature increase from a DSC curve obtained when the temperature is increased to 220 ° C.

(Calculation of the ratio of high-temperature melting heat amount of polypropylene-based expanded particles)
The ratio of the high-temperature side melting heat quantity is measured by using a differential scanning calorimeter DSC [Seiko Instruments Co., Ltd., DSC6200 type], and polypropylene resin foamed particles 5 to 6 mg at a heating rate of 10 ° C./min at 40 ° C. Was calculated from the DSC curve (see FIG. 1) obtained when the temperature was raised from 1 to 220 ° C.

(Reading the maximum value of the differential curve of the DSC curve of polypropylene-based expanded particles)
The maximum value of the differential curve of the DSC curve was calculated by using a differential scanning calorimeter DSC [Seiko Instruments Co., Ltd., DSC6200 type] and increasing the obtained polypropylene resin foamed particles 5-6 mg at a rate of 20 ° C./min. In the curve obtained by differentiating the DSC curve obtained when the temperature was raised from 40 ° C. to 220 ° C. at a temperature rate (see FIG. 2), the temperature at which the maximum value was reached was read.

(Measurement of minimum molding heating steam pressure)
Using a polypropylene foam molding machine [Daisen Co., Ltd., KD345], a block mold having a length of 400 mm, a width of 300 mm, and a thickness of 60 mm consisting of a fixed mold and a movable mold is impregnated with pressurized air in a pressure vessel, and expanded particles Filled with two-stage expanded particles whose internal pressure has been adjusted to 0.2 MPa (absolute pressure) in advance, first expelling the air in the mold with water vapor of 0.1 MPa (gauge pressure), and then at a predetermined molding pressure A polypropylene resin foam molded article was obtained by heating molding (both sides heating) for 10 seconds using heated steam. At this time, by changing the molding pressure every 0.01 MPa, a polypropylene resin foam molded article with good fusion was produced from a polypropylene resin foam molded article with poor fusion.
The lowest molding pressure at which the obtained foamed molded product was divided to obtain a molded product fused without removing each particle was defined as the lowest molding heating steam pressure.

(Surface properties of molded products)
The surface property of the surface of the in-mold foam molded product obtained by in-mold foam molding using a block mold at the minimum molding heating steam pressure was evaluated according to the following criteria.
○: There are almost no wrinkles or intergranularity (intergranularity between polypropylene resin foam particles), the surface irregularities are not conspicuous, and it is beautiful.
(Triangle | delta): There exists a wrinkle and a grain and surface unevenness is somewhat conspicuous.
X: There are wrinkles, intergranular or sink marks, and the appearance is clearly poor.

(Compressive strength)
A test piece having a length of 50 mm, a width of 50 mm and a thickness of 25 mm was cut out from the foamed molded product obtained using the block mold, and 10 mm using a tensile / compression tester [manufactured by Minebea, TG series] in accordance with NDZ-Z0504. Compressive stress at 50% compression when compressed at a rate of / min was measured.
The compressive stress at 50% compression is a measure of the rigidity of the in-mold foam molded product.

(Molded body density)
Measure the weight W (g) of the test piece before measuring the compressive strength, measure the vertical, horizontal, and thickness dimensions of the test piece with calipers to calculate the volume V (cm ³ ), and the compact density in W / V. Ask. However, it was converted so that the unit would be g / L.

(Fusibility of internal bottom standing wall)
A foam molded body obtained using a box-shaped mold is cut with a depth of 5 mm with a cutter at the center in the thickness direction of the inner bottom surface standing wall, and then the inner bottom surface standing wall is split by hand. By visually observing, the ratio of not the foamed particle interface but the inside of the foamed particle was determined, and the fusing property was determined according to the following criteria.
○: The ratio of internal fracture of the expanded particles is 80% or more.
(Triangle | delta): The ratio of an internal fracture | rupture of an expanded particle is 60% or more and less than 80%.
X: The ratio of the internal fracture of the expanded particles is less than 60% (because the degree of fusion is low, the ratio of the expanded particle interface appearing on the fracture surface is more than 40%).

(Beautiful surface of the outer surface of the standing wall edge)
The surface beauty of the outer peripheral surface of the bottom peripheral edge standing wall of the foam molded product obtained using the box mold was determined according to the following criteria.
○: No sink marks and / or wrinkles are observed on the outer peripheral surface of the bottom peripheral edge standing wall. The space between the foamed polypropylene resin particles (intergranular) is also inconspicuous and beautiful.
Δ: Some sink marks and / or wrinkles are seen on the outer peripheral surface of the bottom peripheral edge standing wall. The space between the foamed polypropylene resin particles (intergranular) is inconspicuous and beautiful.
X: Sink marks and wrinkles are remarkably seen on the outer peripheral surface of the bottom peripheral edge. Or the space between the polypropylene resin expanded particles (intergranular) is conspicuous.

Example 1
<Preparation of polypropylene resin particles>
100 parts of polypropylene resin [Prime Polymer Co., Ltd.] having a 1-butene content of 3.8% by weight and an ethylene content of 0.5% by weight, 0.5 parts by weight of a polyethylene glycol as a hydrophilic compound, a foam core 0.2 parts by weight of talc as an agent was added and mixed. The obtained mixture was melt-kneaded at a resin temperature of 220 ° C. using a twin-screw extruder [manufactured by ON Machinery Co., Ltd., TEX40], and the resulting strand was cooled with water and then cut to obtain a polypropylene resin. Particles (1.2 mg / grain) were produced.
<Production of single-stage expanded particles>
In a pressure-resistant container having an internal volume of 10 L, 100 parts by weight of the obtained resin particles, 2 parts by weight of powdery basic tricalcium phosphate as a dispersant, and 0.05 parts by weight of sodium n-paraffin sulfonate as a dispersion aid are added. 300 parts by weight of an aqueous dispersion medium containing, and 7.5 parts by weight of carbon dioxide gas as a foaming agent were added, and while stirring, the temperature was raised to the foaming temperature shown in Table 1 and held for 10 minutes. The foaming pressure shown in Table 1 was adjusted and held for 30 minutes.
After that, while keeping the internal temperature and pressure constant while injecting carbon dioxide gas, open the valve at the bottom of the pressure vessel and release the aqueous dispersion medium through the orifice plate with a hole diameter of 3.6 mmφ under atmospheric pressure. Thus, polypropylene-based resin expanded particles (single-stage expanded particles) were obtained. Regarding the obtained single-stage expanded particles, the expansion ratio, the calculation of the ratio of the high-temperature side fusion heat amount, and the presence / absence of the maximum value of the differential curve of the DSC curve were read. The results are shown in Table 1.
<Preparation of expanded polypropylene resin particles (two-stage expanded particles)>
The obtained single-stage expanded particles were dried at 80 ° C. for 6 hours, and then impregnated with pressurized air in a pressure-resistant container to adjust the internal pressure to 0.37 MPa (absolute pressure), and then 0.08 MPa (gauge Pressure) was brought into contact with water vapor to effect two-stage foaming.
With respect to the obtained two-stage expanded particles, the expansion ratio, the calculation of the ratio of the high-temperature side heat of fusion, the presence / absence of the maximum value of the differential curve of the DSC curve, and the temperature of the maximum value were read. The results are shown in Table 1.
<Preparation of in-mold foam molding>
An in-mold foam molded article was produced under the conditions shown in (Measurement of minimum molding heating steam pressure), and the minimum molding heating steam pressure was evaluated.
Further, the molded body obtained at the lowest molding heating steam pressure was dried at 75 ° C. for 16 hours and then cured at 23 ° C. for 24 hours, and the surface property evaluation and compressive strength of the molded body were measured. The results are shown in Table 1.

(Examples 2-3)
1-butene content, using a polyolefin resin having changed ethylene content [manufactured by Prime Polymer Co., Ltd.], except that various conditions were changed as shown in Table 1, the same operation as in Example 1, Polypropylene resin particles, one-stage expanded particles, two-stage expanded particles, and in-mold expanded molded articles were obtained and evaluated. The results are shown in Table 1.

Example 4
<Preparation of resin particles> The hydrophilic compound was changed to 0.2 parts by weight of melamine, and various conditions were changed as shown in Table 1. Resin particles, one-stage expanded particles, two-stage expanded particles, and in-mold expanded molded articles were obtained and evaluated. The results are shown in Table 1.

(Examples 5-6)
Using the polypropylene resin particles of Example 1, except that various conditions were changed as shown in Table 1, single-stage expanded particles, double-stage expanded particles, and in-mold expanded molded articles were obtained in the same manner as Example 1. And evaluated. The results are shown in Table 1.
In Example 5, the high-temperature heat ratio of the two-stage expanded particles was 12%, and in Example 6, the high-temperature ratio of the two-stage expanded particles was 28%.

(Examples 7 to 8)
Using the polypropylene resin particles of Example 1, except that various conditions were changed as shown in Table 1, single-stage expanded particles, double-stage expanded particles, and in-mold expanded molded articles were obtained in the same manner as Example 1. And evaluated.
The results are shown in Table 1.

Example 9
<Preparation of Two-Stage Foamed Particles> After obtaining the two-stage foamed particles with the two-stage foaming conditions at the time described in Table 1, the two-stage foamed particles were further impregnated with pressurized air, and the internal pressure was 0.35 MPa ( Absolute pressure) and contact with water vapor of 0.03 MPa (gauge pressure) to obtain three-stage expanded particles.
Moreover, except having changed various conditions as shown in Table 1, operation similar to Example 1 was carried out, and a polypropylene resin particle, a single-stage expanded particle, a 2-stage expanded particle, a 3-stage expanded particle, in-mold expansion Molded bodies were obtained and evaluated. The results are shown in Table 1.

(Examples 10 to 12)
1-butene content, ethylene content, and a polyolefin resin with a changed melting point [manufactured by Prime Polymer Co., Ltd.], except that various conditions were changed as shown in Table 1, the same operation as in Example 1, Polypropylene resin particles, one-stage expanded particles, two-stage expanded particles, and in-mold expanded molded articles were obtained and evaluated. The results are shown in Table 1.

(Comparative Examples 1-2)
By using the polypropylene resin particles of Example 1 and changing various conditions as shown in Table 1, the same procedure as in Example 1 was followed to obtain single-stage foam particles, two-stage foam particles, and in-mold foam moldings. Obtained and evaluated. The results are shown in Table 1.
Here, in Comparative Example 1, the high-temperature heat quantity ratio of the obtained two-stage expanded particles was 8%, and in Comparative Example 2, the high-temperature heat quantity ratio was 33%.

(Comparative Example 3)
By using the polypropylene resin particles of Example 1 and changing the various conditions as shown in Table 1, the same steps as in Example 1 were carried out to obtain single-stage foam particles, two-stage foam particles, and in-mold foam moldings. Obtained and evaluated. The results are shown in Table 1.
The maximum value temperature of the differential curve of the DSC curve of the obtained two-stage expanded particles was 126 ° C. The two-stage expanded particles were in an agglomerated state aggregated between the particles and could not be molded.

(Comparative Example 4)
The same procedure as in Example 1 except that the polypropylene resin particles of Example 1 were used, the foaming agent was changed to iso-butane, and single-stage expanded particles with an expansion ratio of 30 times were obtained under the production conditions shown in Table 1. In this way, an in-mold foam molded article was obtained and evaluated. The results are shown in Table 1.
In addition, the maximum value did not exist in the differential curve of DSC measurement of the obtained single-stage expanded particles.

(Comparative Example 5)
Example 1 except that a polypropylene resin (manufactured by Prime Polymer Co., Ltd.) having a 1-butene content of 7.0% by weight and an ethylene content of 3.0% by weight was used and various conditions were changed as shown in Table 1. In the same manner as above, polypropylene resin particles, one-stage expanded particles, two-stage expanded particles, and in-mold expanded molded articles were obtained and evaluated. The results are shown in Table 1.

(Comparative Example 6)
A homopolypropylene resin (1-butene content 0% by weight, ethylene content 0% by weight) [manufactured by Prime Polymer Co., Ltd.] was used, except that various conditions were changed as shown in Table 1, and the same as in Example 1 By operation, polypropylene resin particles, one-stage expanded particles, two-stage expanded particles, and in-mold expanded molded articles were obtained and evaluated. The results are shown in Table 1.

(Example 13)
Using the two-stage expanded particles produced in Example 1, an in-mold foamed molded article having a thick part and a thin part was evaluated as follows. Using a polypropylene foam molding machine [P-300, manufactured by Toyo Machine Metal Co., Ltd.], the inner bottom surface shown in FIG. A box-shaped in-mold foam molded body having a wall portion was obtained. At this time, the air pressure inside the two-stage expanded particles is adjusted in advance to be 0.30 MPa (absolute pressure), and this is filled into a mold, and first, the air in the mold is blown with 0.1 MPa water vapor. The in-mold foam-molded article was obtained by ejecting and then heat-molding (both-side heating) for 10 seconds using heating steam having the steam pressure shown in Table 2.
Here, the box-shaped outer dimensions of the obtained in-mold foam-molded product are 350 mm long × 400 mm wide × 150 mm high, and the thickness of the bottom surface and the bottom peripheral edge standing wall are all uniform and 15 mm. The inner bottom standing wall portion is located at the center of the bottom in the longitudinal direction of the box-shaped in-mold foam molded body, and equally bisects the internal volume. The thickness of the inner bottom surface standing wall portion is 50 mm, and the height of the inner bottom surface standing wall portion is 135 mm (= outside height height 150 mm−bottom surface thickness 15 mm) which is the same as the height of the bottom peripheral edge standing wall portion.
With respect to the obtained in-mold foam molded article, the fusing property of the inner bottom standing wall portion and the surface beauty of the bottom peripheral edge standing wall portion outer surface were evaluated. The evaluation results are shown in Table 2.

(Examples 14 to 21, Comparative Examples 7 to 15)
A box-shaped in-mold foam molded article was obtained and evaluated in the same manner as in Example 13 except that the polypropylene resin particles, foamed particles, and various conditions shown in Table 2 or Table 3 were used.
The results are shown in Table 2 or Table 3.

  In Examples 13 to 21, there was a molding heating steam pressure condition in which both the fusion property of the inner bottom standing wall portion and the surface beauty of the bottom peripheral edge standing wall outer surface were good, but in Comparative Examples 7 to 15 There was no molding heating steam pressure condition in which both the fusing property of the inner bottom standing wall portion and the surface beauty of the bottom peripheral edge standing wall outer surface were good.

(Example 22)
A box-shaped in-mold foam molded body was obtained and evaluated by the same operation as in Example 13, except that the thickness of the inner bottom standing wall portion was 18 mm and the molding heating steam pressure was 0.26 MPa (gauge pressure). did. The results are shown in Table 2.

(Example 23)
Example, except that the width of the inner bottom surface standing wall portion is 50 mm, the height of the inner bottom surface standing wall portion is 75 mm lower than the height of the bottom peripheral edge standing wall portion, and the molding heating steam pressure is 0.26 MPa (gauge pressure). In the same manner as in No. 13, a box-shaped in-mold foam molded article was obtained and evaluated. The results are shown in Table 2.

(Example 24)
The height of the box-shaped outer dimensions is 390 mm, the thickness of the inner bottom standing wall is 50 mm, and the height of the inner bottom standing wall is the same as the height of the bottom peripheral wall, which is 375 mm (= outer height 390 mm-bottom thickness) 15mm)
A box-shaped in-mold foam molded article was obtained and evaluated by the same operation as in Example 13 except that the molding heating steam pressure was 0.30 MPa (gauge pressure). The results are shown in Table 2.

(Example 25)
The box-shaped outer dimensions of the in-mold foam molded body were 350 mm long × 400 mm wide × 310 mm high, and the thickness of the bottom surface and the bottom peripheral edge standing wall were all uniform and 10 mm. Further, the thickness of the inner bottom standing wall portion is 60 mm, and the height of the inner bottom standing wall portion is 300 mm (= outside dimension height 310 mm−bottom surface thickness 10 mm) which is the same as the height of the bottom peripheral edge standing wall portion. A box-shaped in-mold foam molded body was obtained and evaluated by the same operation as in Example 13 except that the pressure was 0.30 MPa (gauge pressure). The results are shown in Table 2.

(Comparative Examples 16-18)
A box-shaped in-mold foam-molded article was obtained by the same operation as in Example 22 (with the thickness of the inner bottom standing wall portion being 18 mm) except that the polypropylene resin particles, foam particles and various conditions described in Table 3 were used. And evaluated. The results are shown in Table 3.

Claims (10)

As comonomer copolymerized with propylene, it contains 1-butene and ethylene, the sum of 1-butene content and ethylene content is 1.0 wt% or more, 1-butene content is 6.0 wt% or less, ethylene content Is a polypropylene resin expanded particle having a base resin of a polypropylene resin having a melting point of 140 ° C. or higher and 155 ° C. or lower, and 3.0% by weight or less,
Foaming ratio 20 times or more and 60 times or less,
In a DSC curve obtained by differential scanning calorimetry (DSC) in which the temperature is raised from 40 ° C. to 220 ° C. at a rate of temperature increase of 10 ° C./minute, the low temperature side melting calorie region (Ql) and the high temperature side melting calorie region (Qh) Have two areas,
The differential in which the ratio (Qh / (Ql + Qh) × 100) (%) of the high temperature side heat of fusion is 10% or more and 30% or less and the temperature is increased from 40 ° C. to 220 ° C. at a temperature increase rate of 20 ° C./min. Polypropylene resin foamed particles having a maximum value between 105 ° C. and 120 ° C. in a differential curve of a DSC curve obtained by scanning calorimetry (DSC).   The polypropylene resin expanded particles according to claim 1, wherein the polypropylene resin as the base resin has a melting point of 147 ° C or higher and 153 ° C or lower.   The polypropylene-based resin expanded particles according to claim 1, wherein the expanded polypropylene resin particles are obtained through at least two expansion steps.   A polypropylene resin-in-mold foam-molded article obtained by foam-molding the polypropylene-based resin foam particles according to any one of claims 1 to 3.   An in-mold foam molded product obtained by using a fixed mold and a movable mold has a portion where the shape is formed by only one of the molds when polypropylene resin foam particles are filled in the mold. The polypropylene resin-in-mold foam-molded article according to claim 4, wherein:   In the in-mold foam molded product obtained by using a fixed mold and a movable mold, when the polypropylene resin expanded particles are filled in the mold, the shape of the part formed by only one of the molds is The polypropylene resin in-mold foam-molded article according to claim 5, which has a shape capable of cutting a sphere having a diameter of 20 mm or more and 100 mm or less when the sphere is cut out most from the portion. It consists of a bottom surface and a bottom peripheral edge standing wall part, and is a polypropylene-based resin-in-mold foam-molded body having an interior capable of storing articles,
Having at least one standing wall on the inner bottom surface;
The thickness of the standing wall portion of the inner bottom surface is 1.2 times or more and 5 times or less of the bottom peripheral edge standing wall portion thickness,
The polypropylene-based resin-molded in-mold foam-molded article according to claim 5 or 6, wherein the height of the standing wall portion on the inner bottom surface is not less than 2 times and not more than 30 times the thickness of the bottom surface.   The polypropylene-based resin-in-mold foam-molded article according to claim 7, wherein the inner bottom standing wall portion is a standing wall portion for partitioning an interior in which articles can be stored.   9. The polypropylene resin-in-mold foam-molded molded product according to claim 7 or 8, wherein a transfer mark at the tip of the filling machine remains on an extension line in the height direction of the standing wall portion on the inner bottom surface. The polypropylene resin-in-mold foam-molded product according to any one of claims 7 to 9, wherein the polypropylene-based resin mold-in-mold foam-molded product is a luggage box.

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