JPWO2017154176A1 - Plastic molded product - Google Patents

Abstract

  A resin having a main body and a rib positioned on at least a part of the surface of the main body, wherein a width A of a bottom surface of the rib is 40% or less of a thickness B of the main body in a portion where the rib is positioned Molding.

Description

  The present invention relates to a resin molded product.

  In recent years, for the purpose of reducing the weight of automobiles, replacement of metal parts in resin parts for interior and exterior parts with resin molded products has been progressing.

  Replacing metal parts with resin molded products is an effective way to reduce the weight of automobiles. However, in response to increasing demands for lower fuel consumption and higher performance of automobiles, resin molded products are even more effective. There is a demand for weight reduction. As a method for reducing the weight of the resin molded product, it is possible to reduce the thickness of the resin molded product. However, in view of the necessary strength, it is technically difficult to make the resin molded product thinner. In view of this, a technique has been adopted in which a reinforcing protrusion called a rib formed integrally with the main body of the resin molded product is provided to supplement the strength (see, for example, JP-A-2005-313330).

  Providing ribs in the resin molded product is an effective measure for achieving both a reduction in thickness of the resin molded product and securing of strength. This will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional view schematically showing a cross section of a resin molded product 10 not provided with ribs, and FIG. 2 is a schematic cross-sectional view schematically showing a resin molded product 20 provided with ribs. In FIG. 1, Ba is the width of the main body of the resin molded product 10, and Ha is the thickness of the main body. 2, Bb1 is the width of the main body of the resin molded product 20, Hb1 is the thickness of the main body, Bb2 is the width of the rib, and Hb2 is the thickness (height) of the rib. Here, assuming that Ba = 200, Ha = 30, Bb1 = 200, Hb1 = 20, Bb2 = 20, and Hb2 = 100, the cross-sectional area of the resin molded product 10 is 200 × 30 = 6000, and the resin molded product 20 The area of the cross section is 200 × 20 + 20 × 100 = 6000, and the cross-sectional areas of both are equal.

Next, cross-sectional second moments under the above conditions will be compared. The value of the moment of inertia of the section is calculated by the width of the section x the cube of the thickness of the section / 12. Therefore, the value of the second moment of the resin molded article 10 becomes ^{200 × 30 3/12 = 450000} . On the other hand, the value of the cross-sectional secondary moment of the resin molded product 20 is the sum of the value of the cross-sectional secondary moment calculated for the main body portion and the value of the cross-sectional secondary moment calculated for the rib portion. Therefore, the value of the second moment of the resin molded article 10 becomes ^{(200 × 20 3/12)} + (20 × 100 3/12) = 1800000.

  As described above, although the resin molded product 20 has a thinner main body than the resin molded product 10, providing the rib realizes a second moment of section that greatly exceeds the resin molded product 10 and greatly improves the strength.

However, a resin molded product provided with ribs may impair the appearance by forming a dent called “sink” on the surface opposite to the surface provided with the ribs due to volume shrinkage after cooling of the molded resin.
In view of the above circumstances, the present inventors have an object to provide a resin molded product in which the occurrence of sink marks is suppressed.

Specific means for solving the problems include the following aspects.
<1> a main body and a rib positioned on at least a part of the surface of the main body, and the width A of the bottom surface of the rib is 40% or less of the thickness B of the main body in the portion where the rib is positioned. There is a resin molded product.
<2> The resin molded product according to <1>, wherein the width A of the bottom surface of the rib is 0.8 mm or more.
<3> The resin molded product according to <1> or <2>, wherein the thickness B of the main body is 2.5 mm or more.
<4> The resin molded product according to any one of <1> to <3>, wherein a width A of a bottom surface of the rib is 1.6 mm or less.
<5> The resin molded product according to any one of <1> to <4>, wherein the thickness B of the main body is 4.0 mm or less.
<6> The resin molded product according to any one of <1> to <5>, wherein the resin molded product is formed of a foamed resin.

  According to the present invention, it is an object to provide a resin molded product in which the occurrence of sink marks is suppressed.

It is a schematic sectional drawing which shows typically the cross section of the resin molded product which does not provide the rib. It is a schematic sectional drawing which shows typically the cross section of the resin molded product which provided the rib. It is sectional drawing which shows roughly an example of the part in which the rib is located in a resin molded product.

Hereinafter, embodiments for carrying out the present invention will be described in detail. However, the present invention is not limited to the following embodiments. In the following embodiments, the components (including element steps and the like) are not essential unless otherwise specified. The same applies to numerical values and ranges thereof, and the present invention is not limited thereto.
In this specification, the term “process” includes a process that is independent of other processes and includes the process if the purpose of the process is achieved even if it cannot be clearly distinguished from the other processes. It is.
In the present specification, the numerical ranges indicated by using “to” include numerical values described before and after “to” as the minimum value and the maximum value, respectively.
In the numerical ranges described stepwise in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerical range. Good. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the values shown in the examples.
In the present specification, the content of each component in the composition is the sum of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. It means the content rate of.
In this specification, the term “layer” refers to the case where the layer is formed only in a part of the region in addition to the case where the layer is formed over the entire region. Is also included.

  The resin molded product of the present embodiment has a main body and a rib positioned on at least a part of the surface of the main body, and the width A of the bottom surface of the rib is the thickness of the main body at a portion where the rib is positioned. 40% or less of B (A / B × 100 ≦ 40).

  FIG. 3 is a cross-sectional view schematically showing an example of a portion where the rib is located in the resin molded product of the present embodiment. The rib 1 is formed integrally with the main body 2 so as to protrude from the surface 3 of the main body 2 of the resin molded product, and has a shape that becomes narrower in the protruding direction. In this specification, the “bottom surface of the rib” means a cross section obtained when the rib 1 is cut from the main body 2 where the inclined surface 4 of the rib 1 rises from the surface 3 of the main body 2. The “width of the bottom surface of the rib” means the distance (arrow A) between the inclined surfaces 4 on both sides of the rib 1 on the bottom surface of the rib 1. “The thickness of the main body at the portion where the rib is located” means the thickness (arrow B) of the main body 2 at the portion where the rib 1 is located.

  According to the study by the present inventors, the resin molded product that satisfies the condition that the width A of the bottom surface of the rib is 40% or less of the thickness B of the main body in the portion where the rib is located is not prone to sink due to the provision of the rib. Was found to be suppressed. That is, it has been found that by reducing the width of the bottom surface of the rib provided on the resin molded product and the thickness of the main body so as to satisfy the above conditions, it is possible to achieve a reduction in thickness while ensuring the strength of the resin molded product.

  The width A of the bottom surface of the rib is not particularly limited as long as the above condition is satisfied. From the viewpoint of sufficiently obtaining the reinforcing effect by the ribs, the value of A is preferably as large as possible. For example, it is preferably 0.8 mm or more, and more preferably 1.0 mm or more. From the viewpoint of suppressing the occurrence of sink marks, the value of A is preferably as small as possible. For example, it is preferably 1.6 mm or less, and more preferably 1.3 mm or less.

  The thickness B of the main body in the portion where the rib is located is not particularly limited as long as the above condition is satisfied. From the viewpoint of suppressing the occurrence of sink marks, a larger value of B is preferable. For example, it is preferably 2.5 mm or more, more preferably 2.7 mm or more, and further preferably 3.0 mm or more. From the viewpoint of reducing the thickness of the resin molded product, the value of B is preferably as small as possible. For example, it is preferably 4.0 mm or less, and more preferably 3.5 mm or less.

  From the viewpoint of sufficiently suppressing the occurrence of sink marks, the width A of the bottom surface of the rib is preferably 37% or less, more preferably 35% or less of the thickness B of the main body in the portion where the rib is located. From the viewpoint of sufficiently obtaining the reinforcing effect of the resin molded product by the rib, the width A of the bottom surface of the rib is preferably 22% or more of the thickness B of the main body in the portion where the rib is located, and is 25% or more. Is more preferable.

  The shape when the rib is observed from the protruding direction of the rib is not particularly limited. For example, it may be linear or bent. Further, when a portion defined by a pair of inclined surfaces is considered as one rib, a shape (for example, a lattice shape) by a combination of a plurality of ribs may be used. The height of the rib (the length in the protruding direction of the rib) is not particularly limited. Generally, the height of the rib tends to increase as the width of the bottom surface of the rib increases.

  The number of ribs provided on the surface of the main body of the resin molded product is not particularly limited. In general, the greater the number of ribs and the shorter the distance between ribs, the greater the reinforcing effect of providing ribs.

The size of the resin molded product is not particularly limited. From the viewpoint of realizing the effect of reducing the thickness while maintaining the strength and suppressing the occurrence of sink marks, for example, the area of the main surface (the surface having the largest area) is 180 cm ² or more. Also good.

  The resin molded product is preferably formed of a resin in which at least a part is foamed. By forming at least a part of the resin molded product from a foamed resin, it is possible to reduce the weight even with the same thickness as compared to the case where the resin molded product is formed from a non-foamed resin. Moreover, although the reason is not clear, the occurrence of sink marks tends to be suppressed as compared with the case where the resin is formed from a non-foamed resin.

  When at least a part of a resin molded product is formed of a foamed resin, for example, a portion near the surface of the resin molded product is formed of a non-foamed resin (also referred to as a skin layer), and the inside is a foamed resin May be formed.

  When at least a part of the resin molded product is formed of a foamed resin, the manufacturing method is not particularly limited. For example, the direction in which the movable mold is separated from the fixed mold after a resin material containing a foaming agent is filled in a gap (cavity) between a pair of molds including the movable mold and the fixed mold. The resin material is foamed by increasing the volume of the void filled with the resin material by moving to the core (core back), and by cooling in this state, a resin molded product that is a molded product of the foamed resin is manufactured. (Injection foam molding). At this time, by providing the mold with a recess corresponding to the shape of the rib at a predetermined position, the rib can be integrally formed on the surface of the main body of the resin material. Moreover, the resin molded product of desired thickness can be manufactured by adjusting the movement distance of a movable side metal mold | die.

  The resin used for the production of the resin molded product is not particularly limited. For example, it can be selected from thermoplastic resins generally used for injection molding. Specifically, polyethylene resins, polypropylene resins, composite polypropylene resins, polystyrene resins, polyethylene terephthalate resins, polyvinyl alcohol resins, vinyl chloride resins, ionomer resins, polyamide resins, acrylonitrile / butadiene / styrene. Examples include copolymer resins and polycarbonate resins. Among these, at least one selected from the group consisting of a polypropylene resin, a composite polypropylene resin, and an acrylonitrile / butadiene / styrene copolymer resin is preferable. There may be only 1 type or 2 or more types of resin used for manufacture of a resin molded product.

  When a foaming agent is used for the production of a resin molded product, examples of the foaming agent include organic foaming agents such as azodicarbonamide, inorganic foaming agents such as sodium hydrogen carbonate (also known as sodium bicarbonate, sodium bicarbonate), and the like. At present, in foam molding of automotive interior parts, inorganic sodium hydrogen carbonate is mainly used as a foaming agent, but an organic foaming agent is preferable from the viewpoint of improving coating film performance (warm water resistance, etc.). .

  Examples of the organic foaming agent include azodicarbonamide (ADCA), N, N-dinitrosopentamethylenetetramine (DPT), 4,4-oxybisbenzenesulfonylhydrazide (OBSH), hydrazodicarbonamide (HDCA), and the like. Azodicarbonamide (ADCA) is preferred.

  The resin molded product of this embodiment can be used for various uses. In particular, it can be suitably used for applications in which the appearance of the surface of the resin molded product is important, for example, interior and exterior parts of automobiles. Examples of the interior and exterior parts of automobiles include a side molding, a locker molding, and a bumper. Among them, it can be suitably used as an interior / exterior part that has a high surface smoothness, such as a paint finish, and is easily noticeable in sink marks.

(1) Production of test resin molded product 1 Resin material for producing a test resin molded product by mixing 100 parts by mass of a polypropylene resin as a resin and 2 parts by mass of azodicarbonamide (ADCA) as a foaming agent Was prepared. Using this resin material, a test resin molded product 1 was produced by injection foam molding.

  As a mold used for producing the test resin molded product 1, a pair of molds including a movable mold that simulates the shape of an automobile rocker molding and a fixed mold are used. The fixed-side mold was provided with recesses corresponding to the shape of ribs at arbitrary 30 locations, and 30 ribs (ribs 1 to 30) were formed on the surface of the main body of the test resin molded product 1. Table 1 shows the width (mm) of the bottom surface of each of the ribs 1 to 30.

  The injection foam molding conditions were a mold temperature of 50 ° C., a cylinder temperature of 220 ° C., a cooling time of 15 seconds, and a resin material temperature of 220 ° C. during injection. The interval between the movable mold and the fixed mold before injection of the resin material was 1.9 mm, and the movable mold was not moved after injection and the resin material was not foamed.

(2) Production of test resin molded product 2 Test resin molded product 1 except that after the resin material was injected, the movable mold was moved away from the fixed mold (core back) to foam the resin material. In the same manner as above, a test resin molded product 2 was produced. The distance between the molds after the core back (the thickness of the main body of the resin material) was 3.2 mm.

(3) Production of test resin molded product 3 Test resin molded product 1 except that after the resin material was injected, the movable side mold was moved away from the fixed side mold (core back) to foam the resin material. In the same manner as above, a test resin molded product 3 was produced. The distance between the molds after the core back (the thickness of the main body of the resin material) was 2.8 mm.

(4) Sinking determination About the produced resin molded products for test 1 to 3, the surface opposite to the surface on which the ribs 1 to 30 are provided is observed, and the place corresponding to the location where the ribs 1 to 30 are located. Whether or not sink marks were generated was examined and evaluated according to the following criteria. The results are shown in Table 1.

When there is no visible sink mark ... A
Visible sink marks are generated, but it can be improved by molding conditions etc ... B
When visible sink marks have occurred and it is recognized that improvement is difficult due to molding conditions, etc ...

  As shown in Table 1, when the width A of the bottom surface of the rib is 40% or less of the thickness B of the main body in the portion where the rib is located, there is no visible sink mark or the visible sink mark. Even if this occurred, it was recognized that improvement was possible depending on molding conditions. On the other hand, when the width A of the bottom surface of the rib exceeds 40% of the thickness B of the main body at the portion where the rib is located, visible sink marks that are recognized as difficult to improve due to molding conditions and the like have occurred. From the above results, it was found that according to the present invention, a resin molded product in which the occurrence of sink marks is suppressed is provided.

Claims (6)

  A resin having a main body and a rib positioned on at least a part of the surface of the main body, wherein a width A of a bottom surface of the rib is 40% or less of a thickness B of the main body in a portion where the rib is positioned Molding.   The resin molded product according to claim 1, wherein a width A of a bottom surface of the rib is 0.8 mm or more.   The resin molded product according to claim 1 or 2, wherein a thickness B of the main body is 2.5 mm or more.   The resin molded product according to any one of claims 1 to 3, wherein a width A of a bottom surface of the rib is 1.6 mm or less.   The resin molded product according to any one of claims 1 to 4, wherein a thickness B of the main body is 4.0 mm or less.   The resin molded product according to any one of claims 1 to 5, wherein the resin molded product is formed of a resin in which at least a part is foamed.