JP3776346B2 - Manufacturing method of double-layer foam blow molding - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a two-layer foam blow molded article such as a duct in which a foam layer is formed in an outer layer portion and a solid layer is formed in an inner layer portion.
[0002]
[Prior art]
When producing a blow molded article such as a duct, it is desirable that the inner surface of the duct be as smooth as possible so that air does not interfere with the flow of air. Ideally, the outer surface of the duct should be made of a foam layer or the like so as to increase heat insulation and prevent condensation. However, it was difficult to make the inner surface of the duct smooth with a foam molded duct having only a foam layer.
For this reason, a composite duct having composite characteristics that cannot be obtained by a single foam layer or solid layer alone is required by combining the two types of properties of the inner layer being a solid layer and the outer layer being a foam layer. A double-layer foam blow molded duct having an inner layer that secures a surface and a foam layer that enhances heat insulation in the outer layer is desired and has been put to practical use.
[0003]
[Problems to be solved by the invention]
However, in order to form the two-layer foam blow molding duct or the like composed of a solid layer and a foam layer, it has been necessary to use a multilayer molding machine. That is, if two-layer foam blow molding is to be performed, a molding machine composed of a die head capable of simultaneously extruding each parison and two extruders is required. The blow molding machine capable of extruding the two-layer parison is not a general-purpose machine and has an economic problem of capital investment.
Even when a foam blow-molded product is molded with a single-layer molding machine, a skin layer can be formed on the outer surface and the inner surface of the product. Therefore, strictly speaking, it can be said that a three-layer product can be formed. However, the skin layer was thin, and the irregularities of the foam layer came out to the surface of the skin layer as they were, and the smoothness of the inner surface could not be maintained.
[0004]
The present invention solves the above-mentioned problems, and uses a general-purpose molding machine for single-layer parison extrusion to form a parison outer layer into a foam layer and a parison inner layer into a solid layer, and to make the inner surface of the parison inner layer smooth An object of the present invention is to provide a method for producing a foamed blow molded article.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the gist of the invention described in claim 1 is that a pair of split molds of a blow mold are opened, and a foam parison is introduced from a die head by chemical foaming or mechanical foaming. The mold is closed, and then low-pressure air is blown into the parison accommodated in the blow mold so that the parison follows the mold surface, and the outer parison layer is cooled from the mold surface through the outer surface of the parison in contact with the mold surface. Then, the outer parison layer is molded and solidified in a foamed state with bubbles, and then, by blowing high pressure air into the parison, the bubbles existing in the inner parison layer still softened are eliminated, and the inner parison layer is solidified. The present invention resides in a method for producing a two-layer foamed blow-molded product, characterized by molding into layers.
A method for producing a two-layer foamed blow molded article according to a second aspect of the present invention is the method according to the first aspect, wherein the pressure of the low-pressure air is in the range of 80 kPa to 100 kPa and the pressure of the high-pressure air is in the range of 500 kPa to 600 kPa. And
[0006]
As in the first aspect of the present invention, when low pressure air is blown and the outer parison layer is molded and solidified in a foamed state, and then high pressure air is blown into the parison inner layer that is still in a softened state, The foam can be eliminated by crushing it, and the inner parison layer can be formed into a solid layer, so even if you do not use a multi-layer molding machine, there are two layers of foam blows with the outer layer part of the foam layer and the inner layer part of the solid layer. Molded products can be molded.
If the pressure of the low pressure air is in the range of 80 kPa to 100 kPa and the pressure of the high pressure air is in the range of 500 kPa to 600 kPa as in the invention of the second aspect, the product is stabilized and the foam layer is formed smoothly on the inside. It becomes possible to mold a double-layer foam blow molded product having a solid layer with a smooth inner surface.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the manufacturing method of the two-layer foam blow molded article of the present invention will be described in detail. FIGS. 1-6 is one form of the manufacturing method of the two-layer foam blow molded article which concerns on this invention, FIG. 1 is explanatory sectional drawing which led the foam parison to the blow mold in a mold open state, FIG. FIG. 3 is an explanatory cross-sectional view in which the mold is closed from the state 1, FIG. 3 is an explanatory cross-sectional view immediately after low pressure air is blown into the parison from the state in FIG. 2, and the parison is pressed against the mold surface. FIG. 5 is an enlarged cross-sectional view around the mold surface taken along line AA in FIG. 3. 5 is an explanatory cross-sectional view showing a state in which high-pressure air is blown into the parison from the state of FIG. 4, and FIG. 6 is an enlarged cross-sectional view around the mold surface after a lapse of time from the state of FIG. FIG.
[0008]
The manufacturing method of the two-layer foam blow-molded product of the present invention is a method for producing a two-layer foam blow-molded product using, for example, a general-purpose molding machine as shown in FIGS.
First, the foam parison 2 is extruded into a tubular shape from a die head 1 onto a thermoplastic resin material (here, polypropylene). The extruded parison 2 descends to the blow mold 5 in the mold open state arranged under the die head 1. The foam parison 2 in a softened state is introduced from the die head 1 into the pair of split molds 5a and 5b in the mold open state (FIG. 1). Here, the gas generation method for making the foamed parison state includes a foaming agent decomposition method (chemical foaming) in which a foaming agent is mixed into a resin base material to form bubbles 33 by thermal decomposition or the like, or nitrogen gas without using a foaming agent There is a mechanical mixing method (mechanical foaming) or the like in which the above is mixed, but the type of the present invention is not limited.
[0009]
Next, the mold is closed, and the parison 2 is sandwiched between the split molds 5a and 5b and accommodated in the blow mold 5 as an internal parison 3 (hereinafter simply referred to as “parison 3”) as shown in FIG. When the mold is closed, the upper and lower pinch-off portions 56 and 57 cut off the parison 2 at the same time, and simultaneously perform fusion sealing. In the present embodiment, the blow pin 6 of the blowing device protrudes from the bottom to the top in the lower pinch-off portion 57 so that the tip of the blow pin 6 reaches the hollow chamber 34 of the parison 3. The parison 3 confined in the blow mold 5 is in a state where the bubbles 33 are dispersed in the softened resin.
[0010]
After completing the mold closing, subsequently, low pressure air is blown from the blow pins 6 into the parison 34 accommodated in the blow mold 5. Then, the parison 3 is brought into close contact with the mold surface 51 which is a cavity surface (FIG. 3). The parison 3 housed in the blow mold 5 expands when low-pressure air is blown and is pressed against the mold surface 51 (FIG. 3).
Here, the pressure _{P 1} of the low-pressure air is preferably in the range of 80KPa～100kPa. Within the range of 80 kPa to 100 kPa, when the pressure is less than 80 kPa, the air between the mold surface 51 and the parison 3 is efficiently extracted while the surface quality of the parison outer layer 31 is stabilized at the pressure P ₁ . Becomes difficult. On the other hand, when the pressure exceeds 100 kPa, the bubbles 33 in the outer parison layer 31 are crushed and it is difficult to form a foam layer in the outer parison layer 31.
[0011]
Then, the parison outer layer 31 of the parison 3 in contact with the mold surface 51 is molded and solidified with the foam layer having the bubbles 33 by the cooling action from the mold surface 51 of the blow mold 5. When the parison 3 in the heat softened state is in close contact with the mold surface 51, heat is gradually taken away by heat conduction exclusively through the outer surface of the parison in contact with the mold surface 51. When the predetermined time (10 to 20 seconds) elapses, the parison outer layer 31 is cooled from the outer surface side (surface side), and the parison outer layer 31 is cooled and solidified in a foamed state (FIG. 4). Even at a low pressure P ₁ of 80 kPa, it is substantially along the shape of the mold surface 51, and the predetermined thickness of the parison outer layer 31 is solidified to obtain a uniform foamed layer 41. However, the parison inner layer 32 that is separated from the mold surface 51 is not solidified at this stage and is still in a softened state.
[0012]
Subsequently, high pressure air is blown into the parison 3 from the blow pin 6 to increase the pressure (FIG. 5). The bubble gas 33 existing in the parison inner layer 32 on the parison hollow chamber 34 side that is still in the softened state is eliminated from the parison inner layer 32 with high-pressure air and formed into a solid layer 42. The parison inner layer 32 on the parison hollow chamber 34 side is located away from the mold surface 51 and contains the bubbles 33 as described above and maintains a soft state of semi-melting. When high-pressure air is blown in, the pressure P ₂ causes the bubbles 33 in the parison inner layer 32 to be crushed or expelled to solidify. The parison inner layer 32 in the softened state is sandwiched between the solidified parison outer layer 31, that is, the solidified foam layer 41, and the high pressure air in the parison hollow chamber 34, and the bubbles 33 in the parison inner layer 32 are crushed by the pressure of the high pressure air. . Alternatively, it is extruded from the parison inner layer 32. Bubbles 33 located in the parison inner 32, further once formed is assumed to solidification was dissolved in softened resin of the parison the inner 32 at a rising pressure P ₂ from the low pressure air to the high pressure air. The reason is not clear, but in any case, it has been confirmed that the bubbles 33 in the parison inner layer 32 disappear by actually switching from the low pressure air to the high pressure air.
[0013]
The pressure _{P 2} of the high pressure air is preferably in the range of 500KPa～600kPa. Within the range of 500 kPa to 600 kPa, if the pressure is less than 500 kPa, the pressure is not sufficient, which causes a problem that the solid layer 42 is difficult to be formed on the parison inner layer 32, while if it exceeds 600 kPa, the parison outer layer that is not yet completely solidified This is because there is a problem in that all the bubbles 43 of the foam layer 41 forming 31 are crushed.
[0014]
Thus, the parison inner layer 32 becomes a solid layer or solid state in which the bubbles 33 disappear. Thereafter, the parison inner layer 32 is deprived of heat from the mold surface 51 and solidifies in the state of the solid layer 42, and the parison 3 becomes the blow molded product 4. The desired two-layer foamed blow-molded article 4 is obtained in which the foamed layer 41 is formed on the outer parison layer 31 and the solid layer 42 is formed on the inner parison layer 32 positioned on the inner side.
[0015]
In the figure, reference numerals 30 and 40 denote boundary surfaces between the foam layer 41 and the solid layer 42, and reference numerals 35 and 45 denote skin layers formed on the surface of the parison outer layer 31. The “solid layer” and “solidification” referred to in the present invention are of course sufficient if the solid layer can be completely solidified, but even if bubbles 43 remain in a part of the solid layer 42 obtained from the parison inner layer 32, If it can be visually recognized that the number of bubbles 43 is significantly smaller than the number of bubbles 43 in the foam layer 41 formed of the outer parison layer, it is considered that the solid layer has been made solid.
[0016]
The low pressure air, each blow time by high pressure air, for example, polypropylene blow-molded article, the cooling can be molded by setting the 30 seconds, As for when the product thickness is 1.0 mm, the low pressure P ₁ ( 80 kPa) for 15 seconds and then high pressure P ₂ (500 kPa) for 15 seconds. When blow molding is performed under such setting conditions, a two-layer foam blow-molded product 4 is obtained in which the foamed layer 41 composed of the parison outer layer 31 is 0.5 mm thick and the solid layer 42 composed of the parison inner layer 32 is 0.5 mm thick. The heating temperature condition of the extruder is the same as that of ordinary blow molding, and is performed at 180 ° C to 200 ° C.
The thickness distribution ratio between the foam layer 41 of the outer parison layer and the solid layer 42 of the inner parison layer can be variously changed by controlling the blow time with low-pressure air and the subsequent blow time with high-pressure air.
[0017]
According to the method for producing a two-layer foamed blow molded article configured as described above, a two-layer molded article can be obtained with an inexpensive general-purpose molding machine without using a two-layer molding machine at the time of molding. Conventionally, when a foaming layer is molded, a blow pressure of 500 kPa to 600 kPa is usually applied. First, the blow pressure is set to a low pressure of 80 kPa to 100 kPa to form the foam layer 41 on the outer layer side, and then 500 kPa at a predetermined timing. By controlling the pressure increase to a pressure of ˜600 kPa, the solid layer 42 can be easily manufactured on the inner layer side. Since the two-layer foam blow-molded product 4 is formed in which the outer parison layer 31 is the foam layer 41 and the inner parison inner layer 32 is the solid layer 42, the inner surface side is smooth without being affected by the unevenness of the outer foam layer 41. become.
When such a two-layer foamed blow molded product 4 is used for a duct or the like, the foamed layer 41 of the parison outer layer 31 enhances heat insulation performance and makes it difficult to condense, and the inner surface of the solid layer 42 of the parison inner layer 32 is smooth. This is extremely beneficial because the fluid in the duct flows smoothly. Further, when the blow-molded product is composed of only the foam layer, the performance such as bending elasticity is deteriorated. However, if the solid layer 42 is present in the inner layer portion as in the present invention, the performance degradation can be suppressed.
Further, the pressure of the low pressure air _{P 1} according to the blow molding in the range of 80KPa～100kPa, the pressure _{P 2} of the high pressure air if the range of 500KPa～600kPa, the foam layer 41 to the outside by quality stability inside The two-layer foamed blow molded product 4 having the smooth inner surface 42 can be easily manufactured.
[0018]
In addition, in this invention, it is not restricted to what is shown to the said embodiment, According to the objective and a use, it can change variously in the range of this invention. The shape, size, number, material, and the like of the die head 1, the parison 2, the parison outer layer 31, the parison inner layer 32, the blow molding die 5, the blow pin 6 and the like can be appropriately selected according to the application. For example, in the embodiment, the lower blow that pushes the blow pin 6 from below is used to inflate the parison 3 after the mold is closed, but an upper blow, a horizontal blow, or the like may be used. In the prior art and embodiments, a duct is taken as an example of a two-layer foam molded article, but it is not limited to this.
[0019]
【The invention's effect】
As described above, the method for producing a two-layer foamed blow molded article of the present invention can easily produce a two-layer foamed molded article having a parison outer layer as a foam layer and a parison inner layer as a solid layer while using a single general-purpose molding machine. It can be molded and exhibits excellent effects such as the ability to keep the inner surface of the inner solid layer smooth.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory cross-sectional view in which a foamed parison is led to a blow mold in an opened state in one embodiment of a method for producing a two-layer foam blow molded article according to the present invention.
FIG. 2 is an explanatory sectional view in which the mold is closed from the state of FIG. 1;
3 is an explanatory cross-sectional view immediately after low pressure air is blown into the parison from the state of FIG. 2 and the parison is placed along the mold surface. FIG.
4 is an enlarged cross-sectional view around the mold surface after a lapse of time from the state of FIG. 3, and is a view taken along the line AA in FIG.
FIG. 5 is an explanatory cross-sectional view showing a state in which high-pressure air is blown into the parison from the state shown in FIG.
6 is an enlarged cross-sectional view around the mold surface after a lapse of time from the state of FIG. 5, and is a view taken along the line BB in FIG.
[Explanation of symbols]
1 Die head 2 Parison (foaming parison)
3 Parisons (including parison)
31 Outer layer of parison 32 Inner layer of parison 33 Air bubbles (bubble gas)
34 Inside the parison (Parison hollow chamber)
4 Double-layer foam blow molded product 41 Foam layer 42 Solid layer 43 Air bubbles (bubble gas)
5 Blow mold 51 Mold surface

Claims (2)

A pair of split molds of the blow mold are opened, a foam parison by chemical foaming or mechanical foaming is introduced from the die head, the mold is closed, and then into the parison accommodated in the blow mold. The parison is blown along the mold surface by blowing low-pressure air, and the parison outer layer is cooled from the mold surface through the outer surface of the parison that is in contact with the mold surface. A method for producing a two-layer foamed blow-molded product, characterized in that high-pressure air is blown into the parison to eliminate bubbles existing in the parison inner layer still in a softened state, and the parison inner layer is molded into a solid layer . The method for producing a two-layer foam blow-molded product according to claim 1, wherein the pressure of the low-pressure air is in the range of 80 kPa to 100 kPa, and the pressure of the high-pressure air is in the range of 500 kPa to 600 kPa.

Images