JP2886248B2 - In-mold molding method for expanded polypropylene resin particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a bumper core material for an automobile, a food container, a heat insulating material for low-pressure steam piping, a helmet core material, a landfill block material for an embankment method, a tatami core material, and the like. The present invention relates to a molding method for producing a foamed molded article, which expands sufficiently to fill a foamed particle gap generated when the volume is compressed and filled (compression ratio is less than 5 to 40%) into a mold by steam heating, In addition, this is a method for obtaining an excellent molded product having excellent mechanical properties such as compressive strength and further having low heat shrinkage resistance.

[Conventional technology]

Polypropylene resin foam particles for in-mold bead molding,
Alternatively, it is known to produce pre-expanded particles by the docan method (autoclave method) (JP-B-49-2183, JP-B-49-2183).
No. 1344, JP-A-60-49040, JP-A-58-25334, JP-A-62-2
128709, 63-256634, 63-258939, 63-10
Nos. 7516 and 63-183832).

These in-mold bead forming particles are obtained by dispersing polypropylene resin particles in water containing a dispersant in a closed container, and then using a volatile expanding agent or an inorganic gas (air, nitrogen gas, carbon dioxide gas) or a mixed gas of both. Into a closed container,
Thereafter, the dispersion was melted at the melting end temperature of the polypropylene-based resin (the temperature T _E of the high-temperature side of the peak of the DSC curve—plastic material course 7, polypropylene resin, pp. 50-51; Nikkan Kogyo Shimbun, Takagi Kenyuki, Edited by Heizo Sasaki, 1969
Heated to a temperature within 10 ° C. higher range than T _E from 35 ° C. lower temperature than issued Nov. 30, 2009), was held 30 minutes to 1 hour at the same temperature, the valve of the discharge pipe provided in the closed vessel lower portion It is obtained by foaming the particles by releasing them and releasing the resin particles together with water into the atmosphere.

Foamed particles obtained by this docan method include foamed particles having no secondary foaming ability themselves (JP-B-63-24617,
JP-A-60-49040) and pre-expanded particles having their own secondary foaming ability (JP-A-62-128709, JP-A-63-256634,
No. 63-107516, No. 63-158939, No. 63-183832).

Foamed particles that do not have secondary foaming ability themselves are obtained when foamed at a relatively low temperature (those without secondary foaming ability: Tm-20 ° C to Tm-100 ° C, have secondary foaming ability) _{things: Tm-10 ℃ ~T E ~} ; Tm of ... starting resin DSC melting peak temperature), the heat shrinkage by heating (volume shrinkage) is high. This is presumed to be due to the fact that when foaming is carried out at a low temperature, the stretching orientation generated on the cell walls during foaming is large (similar to the physical property that the orientation is greater as the stretching temperature during the production of a stretched film is lower). In molding using particles, it is necessary to increase the pressure inside the cells (pressure aging operation) before molding, or to compress the foamed particles by 40 to 70%, fill them in a mold, and heat them with steam to melt them. It is necessary to perform compression molding (compression filling molding method).

In the former case, a large-volume pressure vessel is required, and there are drawbacks such as the inability to accurately detect the pressure in the air bubbles.In the latter case, it is difficult to obtain a molded article having a desired molded article density. Therefore, it was necessary to produce expanded particles having a low density (high expansion ratio).

Further, a molded article using expanded particles having no secondary expansion ability has a disadvantage that heat shrinkability is large.

On the other hand, for pre-expanded particles having secondary foaming ability,
There is known a method in which a molded product is filled without being compressed in a mold, heated with steam, and foamed to obtain a molded product (Japanese Patent Application Laid-Open No. Sho 62).
-128709, 63-107516, 63-256634, 63-
No. 258939), however, has a drawback that the heat shrinkage of the molded article is large as in the case of a foamed particle molded article having no secondary foaming ability.

The reason is that in the molding method, since the foamed particles are filled into the mold without being compressed, the gap between the particles is large (about 33% void in a true sphere). Foam to fill this gap. At this point, it is presumed that stretching orientation occurs due to secondary foaming on the cell wall, and when the molded body is exposed to a high-temperature atmosphere, remarkable thermal shrinkage occurs due to the relaxation phenomenon of the stretching orientation.

For this reason, the conventional polypropylene resin foam molded article has a drawback that it cannot be used for applications used in a high-temperature atmosphere.

For example, as a core material for automobile bumpers, it is difficult to adopt it for long-term use under harsh conditions such as those found in the desert, making it difficult to adopt it. Is used for hot water piping, but cannot be used for steam piping. In addition, the heat resistance of the molded product in the steam sterilization step is also a problem for food containers.

Japanese Patent Application Laid-Open No. 63-183832 discloses a high-temperature peak heat of fusion of 0.3 to 3.5
A method is disclosed in which foamed particles of l / g are filled into a mold at a compression ratio of 10 to 60%, and steam is heated to obtain a molded body. However, the expanded molded article using the expanded particles having a small amount of high-temperature peak heat of fusion as in the present invention has low mechanical properties such as compressive strength, which is a drawback.

The high-temperature-side peak heat of fusion is the heat required to melt the high-order crystals generated by the higher-order transformation of the crystal structure originally contained in the raw material resin due to the heat history received during the production of the expanded particles. The magnitude of the heat of fusion of the high-temperature peak measured by the differential scanning calorimeter indicates the amount of the higher-order crystals, and is used to improve the mechanical properties such as compressive strength and the shrinkage of the molded product with respect to the mold. Requires some degree of higher order crystals (JP-B-63-24617, JP-B-63-24618, 63-44)
No. 779).

[Means for solving the problem]

The present inventors have conducted intensive studies in order to improve the above-mentioned drawbacks, and as a result, have completed the present invention.

The present invention has a high-temperature peak heat of fusion of 4 cal / g as measured by a differential scanning calorimeter of expanded particles having secondary expansion ability.
The above-mentioned foamed polypropylene resin particles, which are random copolymers of propylene and at least one of olefins having 2 or 4 to 6 carbon atoms, are filled in a mold so as to have a compressibility of 5 to 40%. This is a method for in-mold molding of polypropylene-based resin expanded particles, which is performed by steam heating and molding.

As mentioned above, the heat of fusion at the high temperature peak of the expanded particles is 4 cal
If it is less than / g, the mechanical properties of the obtained molded article will be inferior. The high-temperature peak heat of fusion of the expanded particles is
In accordance with JIS K-7122, when the temperature of 1 to 6 mg of particles is raised from 30 ° C to 220 ° C at a rate of 10 ° C / min with a differential scanning calorimeter, the melting of the crystalline state that the raw material resin originally had Is the amount of heat of fusion of the endothermic peak appearing on the higher temperature side than the endothermic peak based on the above.

Further, a molded article obtained by compression-filling at a compression ratio of less than 5% at the time of filling has a large stretching orientation due to secondary foaming after heating, and a large heat shrinkage. Conversely, when molding at a compression ratio of 40% or more, the cooling time and the molding cycle become longer to obtain a molded product that matches the mold, and the molded product surface melts instantaneously due to the high compression ratio. It is not preferable because steam does not sufficiently reach the central part of the molded body and fusion between particles occurs at the central part of the molded body. In particular, this is a problem when molding thick-walled foams such as civil engineering landfill blocks and building materials having a thickness of 10 cm or more.

(Polypropylene Resin) As the polypropylene resin usable in the present invention, propylene / ethylene (0.5 to 8% by weight) random copolymer, propylene / butene-1 (2 to 15% by weight) random copolymer, propylene / Ethylene (0.3-5% by weight)
Butene-1 (0.5 to 20% by weight) random copolymer, propylene / hexene-1 (2 エ 6% by weight) random copolymer, propylene / 4-methylpentene-1 (1 to 8% by weight) random copolymer And a crystalline polypropylene resin such as a coalesced resin.

Among these, a propylene / butene-1 random copolymer which gives an in-mold foam molded article having particularly excellent compressive strength is preferable, and at the same time, the resin used is one that is hardly stretch-oriented, for example, has a narrow molecular weight distribution. , MFR is 5
~ 25g / 10min is preferred.

As the width of the molecular weight distribution, the Q value (Mw / Mn)
Those with less than 6.0, especially 3.5 to 5.8, are good.

(Production method of expanded particles)

100 parts by weight of a polypropylene resin pellet having a Q value of less than 6.0, 150 to 500 parts by weight of water, a hydrocarbon blowing agent 8 in a container
800 parts by weight, dispersant 0.3-5 parts by weight, dispersing aid 0.05-1
Parts by weight, and disperse this dispersion in polypropylene resin.
Raise the temperature between (Tm-7 ° C) and (Tm-3 ° C) with respect to the peak temperature (Tm) of the DSC curve, maintain at the same temperature for 5 to 80 minutes, and lower than the temperature in the closed container. By releasing the polypropylene-based particles together with water into the pressure region, foamed particles can be obtained.

As a suspending agent, calcium pyrophosphate, magnesium pyrophosphate, calcium phosphate, aluminum oxide and the like are used, and as a suspending aid, sodium dodecylbenzenesulfonate and an ethylene oxide adduct of nonylphenol are used.

The higher the temperature at which the dispersion liquid for accelerating the crystallization of the polypropylene-based resin is maintained and the higher the release temperature, the higher the foamed particles having a high secondary foaming ability can be obtained. In addition, mechanical properties such as compressive strength tend to decrease, and if Tm is exceeded, beads are blocked and are not practical.

(In-mold foam molding)

The molding method used in the present invention may be a filling method such as a cracking filling method or a compression filling method using a pressurized gas so as to have a compression ratio of 5 to 40%. A method is used in which the particles are supplied while being compressed while using a pressurized gas higher than the in-mold pressure and filled, and then the foamed particles are fused by steam heating to form a molded foam molded article. In particular, a pressure detecting device is provided in the transfer conduit portion of the foamed particles supplied into the mold by the pressurized gas, and when the detected pressure of the pressure detecting device becomes higher than the pressure in the mold by a predetermined pressure, It is preferable to use a method in which the compression ratio of the foamed particles can be set to a set value by stopping the supply of the foamed particles into the mold.

After compression-filling to 5% to less than 40% using the above-mentioned method, steam is introduced into a mold, and fusion molding is performed while secondary foaming is performed by steam heating.

The steam pressure in this case is 1.0 to 4.5 kg / cm ² G, depending on the magnification of the expanded particles.

 Hereinafter, the present invention will be described in more detail with reference to examples.

 In the examples, parts and% are based on weight.

Example 1 A sealed container having a Q value of 5.3, an MFR of 10 g / 10 minutes, and a Tm of 150
° C., T _E 162 Butene-1 (8.5%) of ° C. - propylene random copolymer resin pellets 100 parts by weight, 300 parts by weight of water, calcium tertiary phosphate 3.2 parts by weight, as dodecylbenzenesulfonate sodium 0.5 parts by weight blowing agent 10 parts by weight of a mixture of 45% by weight of isobutane and 55% by weight of n-butane were added, and the mixture was stirred to form a dispersion. The mixture was heated to 146 ° C. with stirring, and kept at the same temperature for 10 minutes. While introducing a gas and applying a back pressure of 25 kg / cm ² G, the valve at the lower end of the sealed container was opened, and the dispersion was discharged from a nozzle into a receiving tank under atmospheric pressure to obtain expanded particles.

The bulk density of these expanded particles is 40 g /, the closed cell rate is 82%,
The average cell diameter was 260 μm, the peak heat of fusion measured by DSC was 4.3 cal / g, the heat shrinkage at 140 ° C. for 24 hours was 13%. The foamed particles are compression-filled into the cavity of the mold so as to have a compression ratio of 20%, and then 3.8 kg /
Heating was performed by introducing steam of cm ² G into the cavity for 20 seconds, and after cooling the mold, the mold was released to obtain a molded body.

The density of this molded product is 50g /, and the gap between molded product particles is 4
/ 25cm ² , dimensional shrinkage 2.1%, static compressive strength 4.6kg / cm ² ,
The heat shrinkage after heating at 140 ° C. for 24 hours was 15%.

 The DSC curve obtained in Example 1 is shown in FIG.

Explaining the heat of fusion of the high-temperature side peak based on the drawing,
A straight line is drawn from the straight line a based on the end of melting to the melting start point (point c), a perpendicular line is drawn from the boundary point (b) between the low-temperature peak and the high-temperature peak, and the heat of fusion of the hatched portion on the high-temperature side is calculated as the high-temperature peak calorie. And

Examples 2 to 8 and Comparative Examples 1 to 10 Resins having the characteristics shown in Table 1 were foamed under the conditions shown in the table to obtain pre-expanded particles or expanded particles. These pre-expanded particles or expanded particles are filled in a mold at a compression ratio as shown in Table 2, heated at a steam pressure of ³ to 4.2 kg / cm ² G, then cooled and released from the mold. A molded article having physical properties was obtained.

[Effects of the Invention] By using the present invention, it is possible to obtain a molded product that can be used even in a high-temperature atmosphere, which cannot be obtained by the conventional internal bead foam molding, and the use of the polypropylene resin foam molded article can be expanded.

[Brief description of the drawings]

FIG. 1 is a graph for explaining the peak heat of fusion on the high-temperature side, and shows a DSC curve of the expanded particles obtained in Example 1.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C08L 23:10 (56) References JP-A-63-183831 (JP, A) JP-A-63-256634 (JP, A) JP-A-63-258939 (JP, A) JP-A-60-49040 (JP, A) JP-A-61-43539 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B29C 67 / 20 B29C 44/00-44/60 C08L 23/10

Claims (1)

(57) [Claims] (1) From 30 ° C to 220 ° C with a differential scanning calorimeter.
In the DSC curve obtained when the temperature is raised at a rate of ° C / min, the heat of fusion of the endothermic peak that appears on the higher temperature side than the endothermic peak based on the melting of the crystalline state originally possessed by the raw material resin is 4 cal / g or more. Certain polypropylene-based resin foam particles, which are a random copolymer of propylene and at least one kind of olefin having 2 or 4 to 6 carbon atoms, are placed in a mold in an amount of 5 to 5 mm.
A method for in-mold molding of foamed polypropylene resin particles, characterized in that the foam is filled with steam so as to have a compression ratio of 40% and then heated and molded.