JP2024050304A - Foam molded products, vehicle components and vehicle back doors - Google Patents

Abstract

[Problem] To provide a foam-molded product that can achieve both weight reduction and improved rigidity. [Solution] The foam-molded product has a foamed part in which a first skin layer, a foamed layer, and a second skin layer are laminated in this order, and when the maximum thickness in the foamed part is X, the minimum thickness in the foamed part exceeds 0.625X. [Selected Figure] Figure 3

Description

This disclosure relates to foam molded products, vehicle components, and vehicle back doors.

Since resin structures are lighter than metals, they are widely used as vehicle structural parts, vehicle mounted items, housings for electronic devices, etc. Among resin structures, resin molded products in particular are lighter in weight, and their use in vehicle parts such as automobiles is expected to improve fuel efficiency.
To further reduce the weight of resin molded products, it is effective to make them thinner. However, excessive thinning can lead to a decrease in the rigidity of the resin molded product. In addition, shapes such as ribs and bosses that are used to ensure rigidity can damage the surface appearance of the resin molded product.

As a method for reducing the weight of a resin molded product while maintaining its strength, for example, a foam molding method described in Patent Document 1 is known. In Patent Document 1, after molten resin is injected into a cavity of a molding die formed by a movable die and a fixed die, a foaming process is performed in a state in which the movable die is moved slightly apart (cored back) to obtain a resin molded product. Hereinafter, the resin molded product obtained by the foaming process may be referred to as a foam molded product.
When molten resin is injected into the cavity, the part in contact with the molding die cools and solidifies to form a membrane-like skin layer. When the movable die is then cored back against the fixed die to expand the volume of the cavity, the molten resin covered by the skin layer foams to form a foam layer, producing a foam molded product.
According to the foam molding method, the volume inside the cavity can be expanded to increase the thickness of the foam molded product while keeping the weight constant, thereby making it possible to reduce the weight of the foam molded product and improve its rigidity.

JP 2005-238726 A

Incidentally, if the thickness of the foam-molded product before foaming (cavity before core-back) is the same at every location, the thickness of the foam-molded product changes depending on the angle (pulling angle) between the opening and closing direction of the molding die (core-back direction) and the surface of the foam-molded product. Therefore, when the cross-sectional shape of the foam-molded product becomes complex, depending on the punching angle, there may be some parts of the foam-molded product that cannot be sufficiently thickened, resulting in insufficient strength at those parts. Market demands are for the cross-sectional shape of foam-molded products to become more complex in order to improve design.
Specific examples of foam-molded products with complex cross-sectional shapes include outer and inner panels constituting vehicle tailgates, spoilers, arch moldings, sacco moldings, etc. Since molds with a variety of punching angles are used to form these foam-molded products, they tend to have areas that are insufficient in strength.
The present disclosure has been made in consideration of the above-mentioned conventional circumstances, and aims to provide a foam-molded product that can achieve both weight reduction and improved rigidity, as well as a vehicle component and a vehicle tailgate that use this foam-molded product.

Specific means for achieving the above object are as follows.
<1> A foamed portion in which a first skin layer, a foamed layer, and a second skin layer are laminated in this order,
A foam-molded article having a minimum thickness in the foamed region exceeding 0.625X, where X is the maximum thickness in the foamed region.
<2> A vehicle member comprising the foam-molded article according to <1>.
<3> A vehicle back door having an outer panel and an inner panel provided on an inner side of the outer panel, wherein at least one of the outer panel and the inner panel includes the foam molded product according to <1>.

This disclosure makes it possible to provide a foam-molded product that is both lightweight and has improved rigidity, as well as a vehicle component and a vehicle back door that use this foam-molded product.

1 is a schematic cross-sectional view of a molding apparatus 10 used in a foam molding method. 2 is a diagram showing the state in which resin material R is injected and filled into cavity 14 in molding device 10. FIG. 1 is a diagram showing a state in which the movable mold 16 is cored back in the opening direction relative to the fixed mold 12 in the molding device 10. FIG. This is a schematic cross-sectional view showing an example of a molding apparatus 10 equipped with a mold 17 in which the thickness P of the cavity 14 in region Z' where the mold drawing angle θ is greater than or equal to 30° and less than 90° is thicker than the thickness Q of the cavity 14 in region Y where the mold drawing angle θ is 90°. FIG. 2 is a rear view showing the vehicle back door of the present disclosure. FIG. 6 is an exploded perspective view of the vehicle back door of FIG. 5 .

Embodiments of the present disclosure are described in detail below. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, and do not limit the present disclosure.

In the present disclosure, the numerical range indicated using "to" includes the numerical values before and after "to" as the minimum and maximum values, respectively.
In the present disclosure, in which numerical ranges are described in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages.
In the present disclosure, the terms "layer" and "film" include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.
In this disclosure, the term "lamination" refers to stacking layers, where two or more layers may be bonded together or two or more layers may be removable.
In the present disclosure, the average thickness of a layer or film is defined as the arithmetic mean value of thicknesses measured at five points on the layer or film of interest.
The thickness of the layer or film can be measured by observing the cross section with a stereomicroscope, an electron microscope, etc., observing the foam-molded product with an X-ray CT scan, etc. The thickness of the foam-molded product can also be measured using a measuring tool such as a vernier caliper.

<Foam-molded product and its manufacturing method>
The foam molded article of the present disclosure has a foamed portion in which a first skin layer, a foamed layer, and a second skin layer are laminated in this order, and when the maximum thickness in the foamed portion is X, the minimum thickness in the foamed portion exceeds 0.625X.
According to the foam-molded article of the present disclosure, it is possible to obtain a foam-molded article that is both lightweight and has improved rigidity.
The foam-molded product of the present disclosure is particularly effective in that it is possible to achieve both weight reduction and improved rigidity even in a foam-molded product having a complex cross-sectional shape.
An example of an expansion-molded product having a complex cross-sectional shape is an expansion-molded product having a region where, when comparing the draft angle θ described below for any two regions, the difference in the draft angle θ is 30° or more. Note that ribs and bosses are excluded from the arbitrary region.

Below, an outline of a method for producing a foam-molded product by a foam molding method is explained with reference to the drawings. Note that the sizes of the members in each drawing are conceptual, and the relative relationships between the sizes of the members are not limited to these. In addition, members or parts having similar functions are given the same reference numerals throughout the drawings, and their explanations may be omitted.
FIG. 1 is a schematic cross-sectional view of a foam molding apparatus used in the foam molding method.
As shown in Fig. 1, the molding device 10 includes a fixed mold 12 and a movable mold 16 that is movable relative to the fixed mold 12 in an opening/closing direction A shown by the arrow in Fig. 1 and forms a cavity 14, which is a gap, between the fixed mold 12 and the movable mold 16. Hereinafter, the fixed mold 12 and the movable mold 16 may be collectively referred to as a "mold 17".

The cavity 14 is a gap between the cavity surface 12A and the core surface 16A when the fixed mold 12 and the movable mold 16 are closed. In Fig. 1, the thickness of the cavity 14 is the same L0 at every location.
The cavity 14 corresponds to the shape of the foam-molded product before foaming. In other words, the mold-pulling angle θ formed by the opening/closing direction A and the cavity surface 12A or the core surface 16A shown in Fig. 1 is the same as the mold-pulling angle θ formed by the opening/closing direction A and the surface of the foam-molded product before foaming.

In the cavity 14 , the drawing angle θ formed by the opening/closing direction A and the cavity surface 12 A or the core surface 16 A varies depending on the shape of the cavity 14 .
In region X in Fig. 1, the draft angle θ between the opening/closing direction A and the cavity surface 12A or the core surface 16A is approximately 0°. In region Y in Fig. 1, the draft angle θ between the opening/closing direction A and the cavity surface 12A or the core surface 16A is approximately 90°. In region Z in Fig. 1, the draft angle θ between the opening/closing direction A and the cavity surface 12A or the core surface 16A is an angle greater than 0° and less than 90°.

Furthermore, the molding device 10 includes a gate 18 that penetrates the fixed mold 12 to the cavity 14, and an injection machine 20 that injects and fills the cavity 14 with molten resin material R through the gate 18. The injection machine 20 includes a hopper (supply unit) not shown and a cylinder not shown. In the injection machine 20, a mixture containing resin, foaming agent, additives, etc. is supplied from the hopper (supply unit) to the cylinder, and is stirred in the cylinder with a screw or the like to prepare the resin material R, which is then injected and filled into the cavity 14 through the gate 18 at a predetermined pressure. Note that the injection machine 20 is not limited to the above configuration as long as it can inject and fill the cavity 14 with molten resin material R through the gate 18.

A foam molded product can be manufactured, for example, by injecting a resin material R containing a foaming agent into the cavity 14 of the mold 17, filling the cavity 14 with the resin material, and then moving the movable mold 16 from the fixed mold 12 that constitutes the mold 17 in the opening direction of the movable mold 16 in the opening/closing direction A to expand the volume of the cavity 14.

As shown in FIG. 2, resin material R containing a foaming agent is injected and filled into cavity 14 from injector 20 through gate 18. If resin material R is composed of a thermoplastic resin, resin material R is heated and fluidized before being supplied into cavity 14.

The cylinder temperature of the injection machine 20 is preferably 250°C or less. By setting the cylinder temperature of the injection machine 20 to 250°C or less, it is possible to suppress the escape of foaming gas from the hopper outlet side, and it is easy to obtain effects such as improving and stabilizing the foaming property during molding. The cylinder temperature of the injection machine 20 may be 150°C or more.

The resin material used in the present disclosure is not particularly limited. For example, the resin material used in injection foam molding generally contains a resin and a foaming agent. The resin used in the resin material R includes at least one selected from the group consisting of polyethylene resin, polypropylene resin (PP), composite polypropylene resin (PPC), polystyrene resin, polyethylene terephthalate resin, polyvinyl alcohol resin, vinyl chloride resin, ionomer resin, polyamide resin, acrylonitrile butadiene styrene copolymer resin (ABS) and polycarbonate resin. Among these, at least one selected from the group consisting of polypropylene resin (PP), composite polypropylene resin (PPC) and acrylonitrile butadiene styrene copolymer resin (ABS) is preferred.
The resin material may contain a fiber component as required, such as inorganic fibers, such as carbon fibers, glass fibers, metal fibers, and ceramic fibers, and organic fibers, such as aramid fibers and cellulose fibers.

Examples of foaming agents include organic foaming agents such as azodicarbonamide, and inorganic foaming agents such as sodium hydrogen carbonate (also known as sodium bicarbonate or baking soda). Currently, inorganic sodium hydrogen carbonate is the main foaming agent used in foam molding of automotive interior parts, but organic foaming agents are also used.

Organic blowing agents include azodicarbonamide (ADCA), N,N-dinitrosopentamethylenetetramine (DPT), 4,4-oxybisbenzenesulfonylhydrazide (OBSH), hydrazodicarbonamide (HDCA), etc., with azodicarbonamide (ADCA) being preferred.

The mold 17 is usually at a lower temperature than the temperature of the resin material R being supplied. Therefore, when the resin material R is filled into the cavity 14, the resin material R starts to solidify (form a skin layer) from the part that comes into contact with the mold.

In addition, before injecting the resin material R into the cavity 14, the cavity 14 may be filled with nitrogen gas in advance. In this case, the nitrogen gas may be heated. By heating the nitrogen gas to be filled, a sudden drop in temperature inside the cavity 14 (mold 17) is suppressed, and the foaming property of the resin material R tends to be stabilized. In addition, by heating the nitrogen gas to be filled, the dependence of the foaming power of the resin material R on the outside temperature is suppressed without being affected by the outside temperature, and the foaming property of the resin material R tends to be stabilized.

The temperature of the nitrogen gas filled into the cavity 14 is not particularly limited as long as it is a temperature that can prevent a sudden drop in temperature inside the cavity 14 (mold 17), and from the viewpoint of molding stability, it may be 30°C to 50°C.

Next, as shown in Figure 3, the movable mold 16 is opened a predetermined amount in the opening direction relative to the fixed mold 12 (core back), and the unsolidified resin material R is foamed to form a foam layer 22, thereby obtaining a foam-molded product. As shown in Figure 3, a skin layer 24 (first skin layer and second skin layer) is formed in contact with the cavity surface 12A and the core surface 16A so as to surround the foam layer 22.

Here, the thickness L of the foam-molded product is expressed by the following formula A using the thickness L0 of the foam-molded product before foaming, the core-back amount LB, and the demolding angle θ formed by the opening/closing direction A and the surface of the foam-molded product before foaming (i.e., the demolding angle θ formed by the opening/closing direction A and the cavity surface 12A or core surface 16A).
L = L0 + LB · sinθ ... Equation A

When the thickness of the foam-molded product before foaming is uniform (i.e., when L0 in formula A is uniform), in the region where the drawing angle θ is close to 90°, the thickness L is the thickness L0 plus the core-back amount LB. On the other hand, as the drawing angle θ approaches 0°, the thickness L decreases by an amount corresponding to the drawing angle θ.
For example, the thickness L of the foam-molded product in FIG. 3 is L0 in the region X, L0+LB in the region Y, and L0+LB·sin θ in the region Z.

Below, Tables 1 to 18 show specific examples of the value of L when L0, LB, and θ are changed. Also shown are the value of LB × sin θ, and the ratio (L30°/L90°) between L when the mold drawing angle θ is 30° (L30°) and L when the mold drawing angle θ is 90° (L90°). L0' in Table 18 will be explained later.

The bending rigidity of an object is proportional to the elastic modulus of the object and the cube of the plate thickness. In addition, when comparing the elastic modulus of a foam-molded product before foaming with that of a foam-molded product after core-backing, the elastic modulus of the foam-molded product after foaming is lower than that of the foam-molded product before foaming.
Therefore, it is desirable to set the amount of core back and the thickness of the foamed molded product before foaming so that a specified bending rigidity is obtained, taking into account the increase in strength due to the increased plate thickness caused by the core back and the decrease in the elastic modulus of the molded product due to foaming.
Furthermore, in areas where the demolding angle θ is small and the increase in thickness due to the core back is small, the strength of the foam-molded product can be compensated for by previously increasing the thickness of the foam-molded product before foaming.
For example, the thickness of the foam-molded product before foaming (i.e., the thickness of cavity 14) may be increased according to the demolding angle θ so as to ensure a thickness approximately equal to the thickness in the region of the foam-molded product where the demolding angle θ is close to 90°.
Taking the example where L0 is 1.50 mm and LB is 1.60 mm, L is 3.10 mm in the region where the draft angle θ is 90°, as shown in Table 18. Therefore, in the region where the draft angle θ is less than 90°, L0 is adjusted so that L is 3.10 mm, the same as in the region where the draft angle θ is 90°. By increasing the thickness of L0 in advance to L0' by the difference between L when the draft angle θ is 90° and L when the draft angle θ is less than 90°, it is possible to make L the same as in the region where the draft angle θ is 90°, even in the region where the draft angle θ is less than 90°.
Table 18 also shows a specific example of adjusted L0 (L0') for the region where the draft angle θ is less than 90°, in the case where L0 is 1.50 mm and LB is 1.60 mm in the region where the draft angle θ is 90°. For example, in the region where the draft angle θ is 30°, L0 (1.50 mm) is increased by the difference (0.80 mm) between L (3.10 mm) when the draft angle θ is 90° and L (2.30 mm) when the draft angle θ is 30°, to set L0' to 2.30 mm. This makes it possible to set L to 3.10 mm in the region where the draft angle θ is 30°.
By changing the thickness L0' of the foam-molded product before foaming in accordance with the demolding angle θ, it is possible to suppress a partial decrease in rigidity caused by an insufficient plate thickness of the foam-molded product.

On the other hand, in order to reduce the weight of the foam-molded product, it is preferable that the thickness of the foam-molded product before foaming, which is increased to compensate for the rigidity of the foam-molded product, is small. As a result of intensive research, the present inventors have found that it is desirable to increase L0 in advance in the region where the draft angle is 30° or more and less than 90° so that L in the region where the draft angle is 30° or more and less than 90° approaches L in the region where the draft angle is 90° (more preferably, so that L in the region where the draft angle is 30° or more and less than 90° becomes the same as L in the region where the draft angle is 90°).
For example, as shown in Table 5, when the thickness L0 of the foam-molded product before foaming is uniformly set to 1.00 mm and LB is set to 3.00 mm, the ratio of L (L30°) to L (L90°) (L30°/L90°) is 0.625. Based on this value, the inventors set the minimum thickness in the foamed region to a range exceeding 0.625X, where X is the maximum thickness in the foamed region.
In the present disclosure, when the maximum thickness in the foamed region is X, the minimum thickness in the foamed region may be greater than 0.643X, may be greater than 0.667X, may be greater than 0.688X, may be greater than 0.700X, may be greater than 0.714X, may be greater than 0.722X, may be greater than 0.740X, may be greater than 0.742X, may be greater than 0.750X, may be greater than 0.767X, may be greater than 0.786X, may be greater than 0.800X, may be greater than 0.803X, may be greater than 0.833X, may be greater than 0.848X, may be 0.850X or greater, may be 0.900X or greater, or may be 0.950X or greater. In the present disclosure, when the maximum thickness in the foamed region is X, the minimum thickness in the foamed region may be equal to or less than X.

In the present disclosure, the relationship between the maximum thickness and the minimum thickness in the foamed portion is specified because the foamed portion is a portion where the weight of the foam-molded product is reduced while maintaining rigidity.
In addition, in a foam molded product, if the mold-drawing angle θ is small, there may be a region (e.g., region X in FIG. 3) where no foam layer is formed after core-backing. In particular, a foam layer is difficult to form in a region where the mold-drawing angle θ is less than 30°. In the foam molded product of the present disclosure, when defining the relationship between the maximum thickness and the minimum thickness in the foamed portion, it is not necessary to take into consideration the region where no foam layer is formed (i.e., the region that is not a foamed portion). In particular, the mold-drawing angle θ of a portion such as a rib or boss in the foam molded product is close to 0°, and a foamed portion tends not to be formed.

The foam-molded article of the present disclosure is preferably produced by a foam molding method, but the production method is not particularly limited.
A manufacturing method for a foam molded product of the present disclosure includes, for example, injecting a resin material containing a foaming agent into a cavity of a pair of molds including a fixed mold and a movable mold that is movable in an opening/closing direction relative to the fixed mold and forms a cavity that is a gap between the fixed mold and the movable mold, and after filling the cavity with resin material, moving the movable mold that constitutes the mold in an opening direction from the fixed mold to expand the volume of the cavity, wherein the thickness of the cavity in a region where the draw angle θ between the opening direction and the cavity surface is 30° or more and less than 90° may be thicker than the thickness of the cavity in a region where the draw angle θ between the opening direction and the cavity surface is 90°.

Figure 4 is a schematic cross-sectional view showing an example of a molding apparatus 10 equipped with a mold 17 in which the thickness P of the cavity 14 in region Z' where the draft angle θ between the opening direction A and the cavity surface 12A or core surface 16A is 30° or more and less than 90° is thicker than the thickness Q of the cavity 14 in region Y where the draft angle θ between the opening direction A and the cavity surface 12A or core surface 16A is 90°.
When the thickness P of the cavity 14 is greater than the thickness Q of the cavity 14, it becomes possible to compensate for the lack of strength in the portions of the foam-molded product where the thickness increase due to the core back is small.
In addition, in order to suppress an increase in the weight of the foam-molded product, it is desirable to adjust the thickness P of the cavity 14 so that the thickness of the foam-molded product in region Z' where the demolding angle θ is 30° or more and less than 90° after expanding the volume within the cavity (i.e., after core back) is not thicker than the thickness of the foam-molded product in region Y where the demolding angle θ is 90°.
Specifically, the thickness P of the cavity is preferably in the following range.
Q<P<Q+LB・(1-sinθ)・・・Equation B
In formula B, LB represents the core-back amount.

<Vehicle components and vehicle back doors>
The foam molded product of the present disclosure is useful as a vehicle component for use in, for example, automobiles, railways, and other vehicles. The foam molded product of the present disclosure can be suitably used as at least one of the outer panel and the inner panel in a vehicle back door having an outer panel and an inner panel provided on the vehicle inner side of the outer panel. When attempting to obtain vehicle components such as the outer panel and inner panel, spoiler, arch molding, and sacco molding constituting a vehicle back door by foam molding, due to the diversity of the mold-drawing angles, there are some parts that cannot be sufficiently thickened, and the strength of the parts may be insufficient. By applying the foam molded product of the present disclosure to vehicle components, the occurrence of parts with insufficient strength tends to be suppressed.

5 shows the back door 40 in a state where a back door opening (not shown) of the vehicle body 30, indicated by a two-dot chain line, is closed. The back door 40 is attached to the vehicle body 30 and has a function of opening and closing the back door opening of the vehicle body 30.
The back door 40 includes an inner panel 42 (see FIG. 6), an outer panel 44 (see FIG. 6), and a reinforcing member (not shown).
As shown in FIG. 6 , the inner panel 42 is a resin panel material that constitutes the vehicle interior side of the back door 40 .
6, the outer panel 44 is a resin panel material that constitutes the vehicle outer side portion of the back door 40. The outer panel 44 is attached to the inner panel 42. As an example, the outer panel 44 is attached to the inner panel 42 using an adhesive, but the present disclosure is not limited thereto.
Further, a rear window glass 46 serving as door glass is attached to the back door 40.

REFERENCE SIGNS LIST 10 molding device 12 fixed mold 14 cavity 16 movable mold 17 mold 22 foam layer 24 skin layer 30 vehicle body 40 back door 42 inner panel 44 outer panel 46 rear window glass

Claims (3)

a foamed portion in which a first skin layer, a foamed layer, and a second skin layer are laminated in this order;
A foam-molded article having a minimum thickness in the foamed region exceeding 0.625X, where X is the maximum thickness in the foamed region. A vehicle component comprising the foam molded product according to claim 1. A vehicle back door comprising: an outer panel; and an inner panel provided on an inner side of the outer panel, wherein at least one of the outer panel and the inner panel includes the foam molded product according to claim 1.