JP7181451B2 - Foam duct manufacturing method - Google Patents

Description

The present invention relates to a method for manufacturing foam ducts.

A dashboard of an automobile is provided with a duct (called an "instrument panel duct") for ventilating air from an air conditioner. As such a duct, a foam duct made of a foam molding is sometimes used in consideration of heat insulation and quietness (Patent Document 1). The foam duct is formed by foam blow molding or the like.

JP 2015-124380 A

By the way, when cold air is circulated in the duct in a high-humidity environment, a problem may arise in that dew condensation water produced by dew condensation on the outer surface of the duct drips.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and provides a method for manufacturing a foam duct that can suppress dripping of condensed water.

According to the present invention, a method for manufacturing a foam duct comprises a molding step and a surface roughening step, wherein the molding step includes molding a foam parison to form a foam molded body, and the surface roughening step. Then, roughening is performed in at least a part of the roughened region of the outer surface of the foam molded article, and the roughening is performed so that the adhesion energy of water droplets in the roughened region is 0.030 mJ/m ² or more. A method is provided, which is performed so that

As a result of intensive studies by the present inventors, it was found that after forming a foam molded article, the surface was roughened so that the adhesion energy of water droplets in the roughened region was 0.030 mJ/m ² or more, and dew condensation occurred. The inventors have found that dripping of water can be greatly suppressed, and have completed the present invention.

Various embodiments of the present invention are illustrated below. The embodiments shown below can be combined with each other.
Preferably, the method as described above, wherein said roughening is performed by sanding said outer surface in said roughened region.
Preferably, in the method described above, the roughening is performed so that the adhesion energy is 0.080 mJ/m ² or less.
Preferably, in the method described above, the roughening is performed so that the maximum cross-sectional height Rt is 70 to 200 μm.
Preferably, in the method described above, the foamed molded article has an expansion ratio of 1.5 to 5 times.
Preferably, in the method described above, the foamed molded body formed in the molding step has a tubular portion and a bag portion, the bag portion is provided at an end of the tubular portion, and the cutting step is performed. wherein, in the cutting step, the cylindrical portion is cut.
Preferably, the method as described above, wherein the cutting step is performed before the roughening step.

1 shows an example of a molding machine 1 that can be used to manufacture foam ducts according to one embodiment of the present invention. 1 is a perspective view showing a foam molding 10 for manufacturing a foam duct; FIG. Fig. 2 is a perspective view of the foam molded article 10 after the cutting step; 4A and 4B are explanatory diagrams showing a method of measuring adhesion energy. FIG. 2 is a conceptual diagram for explaining a sound absorption coefficient measuring device; It is a graph showing the measurement result of a sound absorption coefficient.

Embodiments of the present invention will be described below. Various features shown in the embodiments shown below can be combined with each other. In addition, the invention is established independently for each characteristic item.

1. Configuration of Molding Machine 1 First, a molding machine 1 that can be used to manufacture a foamed duct according to an embodiment of the present invention will be described with reference to FIG. The molding machine 1 includes a resin supply device 2 , a head 18 and a split mold 19 . The resin supply device 2 includes a hopper 12 , an extruder 13 , an injector 16 and an accumulator 17 . The extruder 13 and the accumulator 17 are connected via a connecting pipe 25 . The accumulator 17 and the head 18 are connected via a connecting pipe 27 .
Each configuration will be described in detail below.

<Hopper 12, Extruder 13>
The hopper 12 is used to charge the raw material resin 11 into the cylinder 13 a of the extruder 13 . Although the form of the raw material resin 11 is not particularly limited, it is usually in the form of pellets. The raw material resin 11 is, for example, a thermoplastic resin such as polyolefin. Polyolefins include low-density polyethylene (LDPE), linear low-density polyethylene, high-density polyethylene (HDPE), polypropylene, ethylene-propylene copolymers and their mixtures and the like. The raw material resin 11 preferably contains HDPE and LDPE, and the mass ratio of HDPE and LDPE is preferably 35:65 to 70:30. The raw material resin 11 is fed from the hopper 12 into the cylinder 13a, and then heated in the cylinder 13a to be melted into a molten resin. Further, it is conveyed toward the tip of the cylinder 13a by the rotation of the screw arranged in the cylinder 13a. The screw is arranged in the cylinder 13a, and conveys the molten resin while kneading it by its rotation. A gear device is provided at the proximal end of the screw, and the screw is rotationally driven by the gear device.

<Injector 16>
The cylinder 13a is provided with an injector 16 for injecting a foaming agent into the cylinder 13a. The blowing agent injected from the injector 16 includes physical blowing agents, chemical blowing agents, and mixtures thereof, but physical blowing agents are preferred. As physical blowing agents, inorganic physical blowing agents such as air, carbon dioxide gas, nitrogen gas, and water, organic physical blowing agents such as butane, pentane, hexane, dichloromethane, and dichloroethane, and supercritical fluids thereof are used. be able to. As the supercritical fluid, it is preferable to use carbon dioxide, nitrogen, or the like. Nitrogen has a critical temperature of −149.1° C. and a critical pressure of 3.4 MPa or higher, and carbon dioxide has a critical temperature of 31° C. and a critical pressure of 3.4 MPa. It is obtained by making it 7.4 MPa or more. Chemical foaming agents include those that generate carbon dioxide through a chemical reaction between an acid (eg, citric acid or its salt) and a base (eg, sodium bicarbonate). The chemical blowing agent may be injected from hopper 12 instead of injected from injector 16 .

<Accumulator 17, Head 18>
A molten resin 11 a obtained by melt-kneading a raw material resin and a foaming agent is extruded from a resin extrusion port of a cylinder 13 a and injected into an accumulator 17 through a connecting pipe 25 . The accumulator 17 has a cylinder 17a and a piston 17b slidable inside the cylinder 17a, and the molten resin 11a can be stored in the cylinder 17a. By moving the piston 17b after a predetermined amount of the molten resin 11a is stored in the cylinder 17a, the molten resin 11a is extruded through the connecting pipe 27 from the die slit provided in the head 18 and suspended to form the foamed parison 23. to form The shape of the foamed parison 23 is not particularly limited, and may be cylindrical or sheet-like.

<Split mold 19>
A foamed parison 23 is guided between a pair of split molds 19 . By molding the foam parison 23 using the split mold 19, the foam molded body 10 as shown in FIG. 2 is obtained. The method of molding using the split mold 19 is not particularly limited, and may be blow molding in which air is blown into the cavity of the split mold 19 for molding. may be vacuum forming in which the foamed parison 23 is formed by depressurizing the pressure, or a combination thereof.

FIG. 2 shows a foam molding 10 for producing foam ducts. The foam molded body 10 has a bag portion 3 . The bag portions 3 are provided at both ends of the cylinder portion 6 . In FIG. 2, the foam molded body 10 does not have a branched structure, but the bag portions 3 may be branched to increase the number of bag portions 3 to three, four or more.

2. Method for Producing Foamed Duct The method for producing a foamed duct according to the present embodiment includes a molding step, a cutting step, and a surface roughening step.

In the molding step, the foamed parison 23 is molded to form the foamed molding 10 having the cylindrical portion 6 and the bag portion 3 . The bag portions 3 are provided at both ends of the cylindrical portion 6 , and the cylindrical portion 6 is closed by the bag portions 3 .

The expansion ratio of the foam molded article 10 is preferably 1.5 to 5 times, more preferably 2 to 3 times. If the foaming ratio is too low, the heat insulating property will be insufficient, and even if the surface is roughened, it will be difficult to increase the adhesion energy. On the other hand, if the expansion ratio is too high, the strength of the foam molded article 10 may be insufficient. Specifically, the expansion ratio is, for example, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 times, and the numerical values exemplified here may be in the range between any two of

By cutting the bag portion 3 in the cutting step, as shown in FIG. Air from the air conditioner flows into the foam molded body 10 through one opening 3a and is discharged through the other opening 3a. In the molding process, the cutting process can be omitted by forming the foam molded body 10 so that the bag portion 3 is not formed.

When cold air flows into the foam molded article 10, the foam molded article 10 is cooled, and dew condensation tends to occur on the outer surface of the foam molded article 10.

If the condensed water generated by the dew condensation drips, it causes a problem such as malfunction of the electronic device, so it is necessary to suppress the dripping of the condensed water. Therefore, in the roughening step, at least a partial roughened region of the outer surface of the foam molded article 10 is roughened. The roughened area may be the entire outer surface of the foam molded article 10, or may be a partial area where dew condensation is likely to occur.

It is important to roughen the surface so that the adhesion energy of water droplets in the roughened region is 0.030 mJ/m ² or more. If this adhesion energy is too small, the suppression of dripping of condensed water will be insufficient.

Adhesion energy can be measured by the following method.
First, as shown in FIG. 4A , 150 μL of water droplets 9 are dropped onto the roughened region 8 of the foam molded article 10 while the roughened region 8 is horizontal. In this state, the contact diameter D of the water droplet 9 is measured.
・Next, as shown in FIG. 4B, the inclination of the roughened region 8 is gradually increased, and the sliding angle α when the water droplet 9 slides down along the roughened region 8 as indicated by the arrow X is measured. .
- The adhesion energy is calculated based on the formula (1). In formula (1), m is the mass of the water droplet 9, and g is the gravitational acceleration.
Adhesion energy = mg sinα/πD (1)

The adhesion energy is, for example, 0.030 to 0.100 mJ/m ² , preferably 0.080 mJ/m ² or less. In order to increase the adhesion energy, it is necessary to increase the degree of surface roughening. Excessive surface roughening tends to cause problems such as poor appearance and reduced strength. Specifically, the adhesion energy is, for example, 0.030, 0.040, 0.050, 0.060, 0.070, 0.080, 0.090, 0.100 mJ/m ² , and exemplified here It may be in a range between any two of the numbers given.

The surface roughening can be performed by any method that allows the adhesion energy to fall within the above range. Sanding means polishing with sandpaper. The larger the grit of the sandpaper (the finer the mesh), the greater the adhesion energy tends to be. This is presumably because the finer the mesh of the sandpaper, the more the abrasive grains detached from the sandpaper penetrate into the dimple-formed air bubbles on the surface and support the dimples from the sides. The number of the sandpaper is preferably #1200 or less, more preferably #1000 or less. This count is, for example, #200 to #1200, #200, #250, #300, #350, #400, #500, #600, #1000, #1200, any of the numerical values exemplified here It may be in a range between the two. Sanding can be done with an electric sander.

Roughening is performed so that the maximum cross-sectional height Rt specified in JIS B 0601:2001 is 70 to 200 μm. When Rt is within this range, condensation water dripping is particularly characteristic, and sound absorption is particularly excellent. Rt is specifically, for example, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200 μm, and between any two of the numerical values exemplified here may be within the range of

The roughening step may be performed before or after the cutting step. The roughening step is preferably performed after the ablation step, as the adhesion energy of the planarized region may change.

Using the molding machine 1 shown in FIG. 1, foam molded articles 10 of Examples and Comparative Examples shown in Table 1 were produced. The inner diameter of the cylinder 13a of the extruder 13 was 50 mm, and L/D=34. For the raw material resin, a propylene homopolymer (manufactured by Borealis AG, trade name "Daploy WB140") and long-chain branched polypropylene (manufactured by Japan Polypropylene Corporation, trade name "EX6000K") were used at a mass ratio of 30:70. LDPE base masterbatch containing 20 wt% sodium bicarbonate foaming agent as a nucleating agent (manufactured by Dainichiseika Kogyo Co., Ltd., trade name "Fine Cell Master P0217K") for 100 parts by mass of resin. .0 parts by weight and 1.0 parts by weight of an LLDPE base masterbatch containing 40 wt% carbon black as a colorant. The temperature of each part was controlled so that the temperature of the foamed parison 23 was 190 to 200.degree. The blowing agent was injected through injector 16 using _N2 gas. The injection amount of the foaming agent, the extrusion speed of the molten resin 11a, and the gap between the die slits of the head 18 were set so that the foaming ratio was the value shown in Table 1 and the average thickness was 2.5 mm. In addition, in Table 1, in the comparative example having an expansion ratio of 1, no foaming agent was injected.

The foamed parison 23 formed under the above conditions was placed between the split molds 19 and subjected to blow molding to produce the foamed molded article 10 shown in FIG. Next, the bag portions 3 at both ends of the cylindrical portion 6 were cut off to form openings 3a at both ends.

Next, sanding was performed on the outer surface of the cylindrical portion 6 for the examples and comparative examples in which sanding was “yes”. The sanding was performed by attaching sandpaper of the count shown in Table 1 to an electric sander. Through the above steps, samples of Examples and Comparative Examples were obtained.

For the samples of Examples and Comparative Examples, the adhesion energy and condensation water dropping time were measured, and the appearance was evaluated.

Details of the measurement and evaluation methods are as follows.

<Adhesion energy>
The adhesion energy was measured according to the method described in "2. Manufacturing method of foam duct".

<Condensed Water Drip Time>
The samples of Examples and Comparative Examples were set on a fixing jig placed in a chamber adjusted to 40° C. and humidity of 80%, and 40 m 3 of air at 4° C.±1° C. was introduced into the cylindrical portion 6 from one opening 3 a ^. /h, and flowed out from the other opening 3a. The time from the start of air inflow to the start of dripping of condensed water was measured. A dew condensation time of 20 minutes or longer was regarded as acceptable.

<Appearance evaluation>
The appearance of the samples of Examples and Comparative Examples was observed and evaluated according to the following criteria.
◯: Neither whitening nor thickness unevenness occurred on the sanded surface.
Δ: Thickness unevenness occurred on the sanded surface.
x: Whitening occurred on the sanded surface.

<Sound absorption measurement>
Sound Absorption Coefficient Measuring Device A sound absorption coefficient measuring device will be described with reference to FIG. In this embodiment, a sample 37 is placed in a thin tube 34 of φ29 mm, and sound is output from a speaker 35 . Then, the sound pressures of the output sound and the reflected sound are measured by the microphone 36, and the sound absorption coefficient is measured from the sound pressure attenuation of the output sound and the reflected sound. The sample 37 is placed so that the outer surface of the cylindrical portion 6 faces the microphone 36 side. The output sound of the speaker 35 is varied from 100 to 6000 Hz, and the sound absorption coefficient is measured for each frequency sound.

Measurement of Sound Absorption Coefficient Sound absorption coefficients of the samples of Examples 1 to 3 and Comparative Example 3 were measured. The results are shown in FIG.

<Discussion>
As shown in Table 1, in all the examples in which the adhesion energy was 0.030 mJ/m ² or more, the condensation water dropping time was sufficiently long. On the other hand, in all the comparative examples in which the adhesion energy was less than 0.030 mJ/m ² , the condensation water dropping time was insufficient.

In Comparative Example 4, in which sandpaper with a small number was used for sanding, the adhesion energy and the maximum cross-sectional height Rt were small.

Reference Signs List 1: molding machine 2: resin supply device 3: bag portion 3a: opening portion 6: cylinder portion 8: roughened area 9: water droplets 10: foam molded body 11: raw resin 11a: molten resin 12: hopper 13: extruder 13a: Cylinder 16: Injector 17: Accumulator 17a: Cylinder 17b: Piston 18: Head 19: Split mold 23: Foam parison 25: Connecting pipe 27: Connecting pipe 34: Capillary tube 35: Speaker 36: Microphone 37: Sample

Claims (5)

A method for manufacturing a foam duct, comprising:
Equipped with a molding process and a roughening process,
In the molding step, a foamed parison is molded to form a foamed molded body,
In the roughening step, roughening is performed by sanding the outer surface of at least a partial roughened region of the outer surface of the foam molded body,
The method according to claim 1, wherein the surface roughening is performed so that the adhesion energy of water droplets in the roughened region is 0.030 mJ/m ² or more and the maximum cross-sectional height Rt is 70 to 200 μm . 2. The method of claim 1 , wherein
The method, wherein the roughening is performed so that the adhesion energy is 0.080 mJ/m ² or less. A method according to claim 1 or claim 2 ,
The method, wherein the expansion molding has an expansion ratio of 1.5 to 5 times. The method according to any one of claims 1 to 3 ,
The foam molded body formed in the molding step has a cylindrical portion and a bag portion,
The bag portion is provided at an end of the tubular portion,
Equipped with an excision process,
A method in which the cutting step includes cutting the tubular portion. Claim 4 The method according to
The method, wherein the cutting step is performed before the roughening step.

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