JPWO2008069013A1 - Resin foam suitable for energy absorber - Google Patents

Abstract

To provide a foam having shock absorption characteristics equivalent to that of a rigid polyurethane foam, having a small volume increase due to moisture absorption, and suitable for energy absorbing materials such as a bumper core and a side projection material. The thermoplastic resin foam of the present invention has a load ratio (F70%) / (F20%) of a load at 70% strain (F70%) and a load at 20% strain (F20%) based on a dynamic compression test. Is 0.70 or more and 1.30 or less, and more preferably, the cell-shaped anisotropy ratio is 1.1 or more and 3.0 or less.

Description

  The present invention relates to a resin foam suitable for an energy absorbing material.

  BACKGROUND ART Energy absorbing materials for automobiles are used in various applications such as bumper core materials and side projection materials, and weight reduction is required from the viewpoint of improving fuel consumption and reducing costs.

  When the energy absorbing material receives an impact, the energy absorbing material itself absorbs the impact energy by partial destruction or deformation, so that the protected object is not directly impacted, but a load is still generated by the impact. If this load is too large, the object to be protected is destroyed and the function is lost. Therefore, an energy absorbing material that suppresses the maximum generated load as much as possible is desirable.

  On the other hand, the energy absorption amount is an integration of the impact load and the deformation amount of the energy absorbing material, and a larger impact load can absorb more energy. From these two conflicting events, the most important performance required for the energy absorbing material is to absorb more energy by maintaining a constant load while suppressing the maximum load generated.

  Moreover, as an energy-absorbing material for automobiles, foamed plastic is often used from the viewpoint of lightness. Rigid polyurethane foam is widely known as a foamed plastic having such characteristics. Rigid polyurethane worms exhibit a substantially constant compressive stress from 20% to 70% in the dynamic compression test due to the characteristics of the resin that the cells are vertically long and the brittle fracture is liable to occur. Since it has such characteristics, the impact absorption performance of the rigid polyurethane foam is good, but it is high in cost and has a large volume increase due to moisture absorption, so it is not suitable as a core material for an automobile bumper exposed to the outside air.

  In Patent Document 1, a plurality of thermoplastic extruded strand foams are combined to obtain a foam having higher compressive strength in one direction than the other direction, and impact is applied in the direction in which the compressive strength is higher. To absorb shocks. This foam is shown to have higher compressive strength at 25% strain than a foam of the same material and density. However, such a document only discloses a foam made of polyolefin. Polyolefins have a large temperature dependency of their mechanical properties, and have a drawback that they cannot exhibit sufficient shock absorbing properties at high temperatures in automobiles that have relatively high temperatures. In addition, since polyolefin is poor in brittleness of the resin, it cannot exhibit energy absorption characteristics similar to rigid polyurethane foam.

Patent Document 2 discloses a foam made of a polyolefin resin having a bending stiffness of 6000 to 14000 kgf / cm ² , and the bubble diameter in the thickness direction of the foam is larger than the bubble diameter in the direction perpendicular to the thickness direction. A foam having an elliptical shape is disclosed. However, for the reasons described above, the foam made of polyolefin cannot be expected to have the same energy absorption characteristics as rigid polyurethane foam.

  On the other hand, expandable polystyrene resin is inexpensive and easily obtains an in-mold foam-molded product. Although the volume increase due to water absorption is small, it is not suitable for energy absorbers in automobiles that reach a relatively high temperature and is subject to impact. Since the load at the time increases as the amount of deformation of the material increases, there is a drawback that the impact of the protected object increases.

  In Patent Document 3, as a foamed molded article excellent in shock absorption, compression when the weight average molecular weight is 45,000 to 120,000 and the compression strain is 5% in the compression test defined by JIS-K7220. A polystyrene foam in which the ratio Y / X of the compressive stress Y when the stress X and the compressive strain are 50% is 2.0 or less is disclosed. This indicates that the impact stress is small at the initial stage of impact, but it is not disclosed to absorb a lot of energy by maintaining a constant stress. In general, in a polystyrene foam, the stress at the time of compression when the compression strain exceeds 50% greatly increases. Therefore, it cannot be said that good impact absorbability is exhibited in applications in which further compression strain occurs. Even a material that absorbs a lot of energy is required to exhibit a substantially constant stress from about 20% to about 70% as a compressive strain as an impact absorbing material.

Patent Document 4 includes a polycarbonate resin foam molded product, and a value obtained by dividing the energy absorption amount of the molded product at 50% compression at 80 ° C. by the density of the molded product is 30 (kg · cm / cm ³ ) / An automobile energy absorber that is (g / cm ³ ) or more is disclosed. However, this document only shows that the amount of energy absorption per unit mass of the compact is large, and does not mention compressive stress. It can be very large.

  Patent Document 5 gives a structure in which a foamed molded body is destroyed when subjected to a large impact by dispersing the polyolefin-based resin expanded particles (B) in a foamed body (A) made of a polystyrene-based resin, A thermoplastic resin foam molded article is disclosed in which the ratio of impact load at 20% strain to impact load at 60% strain is 1.6 or less in a dynamic compression test. This document shows performance close to that of polyurethane foam in a dynamic compression test, but only discloses that a constant load is maintained from the time of 20% strain to the time of 60% strain. Furthermore, it is required to maintain a constant load for a longer time.

  Patent Document 6 includes at least one thermoplastic resin foam particle having a three-dimensional network structure and one or more thermoplastic resin particles that are not at least partially melted with the thermoplastic resin foam particle. An energy absorbing material comprising a composite resin molded body and a space in which the composite resin molded body can be scattered during energy absorption is disclosed. This document discloses an energy absorbing material that exhibits a substantially constant compressive stress from 10% strain to 60% strain in a dynamic compression test. In this document, since the composite resin molded body and the space where the composite resin molded body can be scattered, the composite resin molded body needs to be cut, punched, joined, or designed in shape including the scattered space. There is a demand for a material that exhibits good shock absorption performance with the foamed molded product itself without adding such post-processing and shape design.

JP-T-2002-511917 Japanese Patent Laid-Open No. 10-219017 JP 2002-212322 A Japanese Patent Laid-Open No. 11-287277 JP 2004-142260 A JP 2006-68905 A

  An object of the present invention is to provide a foam having shock absorption characteristics equivalent to that of a rigid polyurethane foam, having a small volume increase due to moisture absorption, and suitable for energy absorbing materials such as a bumper core and a side projection material.

That is, the present invention is a value of a load ratio (F _70% ) / (F _20% ) between a load at 70% strain (F _70% ) and a load at 20% strain (F _20% ) based on a dynamic compression test. The thermoplastic resin foam has a volume increase rate of 5% or less when immersed in water for 24 hours.

As a preferred embodiment,
(1) The cell-shaped anisotropy ratio is 1.1 or more and 3.0 or less,
(2) Copolymer (A) comprising aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide (A) 80-30% by weight and aromatic vinyl-vinyl cyanide copolymer (B) 20-70% % Of a foamed thermoplastic resin composition formed by mixing
(3) The aromatic vinyl is styrene,
(4) The unsaturated dicarboxylic acid anhydride is maleic anhydride,
(5) The N-alkyl-substituted maleimide is N-phenylmaleimide,
(6) The vinyl cyanide is acrylonitrile,
(7) The thermoplastic resin foam is produced by an extrusion foam molding method,
It relates to the thermoplastic resin foam described above.

Another aspect of the present invention is the thermoplastic resin foam described above.
(1) Automotive bumper core,
(2) The present invention relates to an automobile side collision pad.

  According to the present invention, it is possible to obtain a thermoplastic resin foam that is low in cost, excellent in energy absorption characteristics, and small in volume change due to water absorption.

The thermoplastic resin foam of the present invention has a load at 70% strain (hereinafter referred to as F _70% ) and a load at 20% strain (hereinafter referred to as F _20% ) based on a dynamic compression test. The value of the ratio (F _70% ) / (F _20% ) is 0.70 or more and 1.30 or less. In order to absorb the energy while suppressing the generated maximum load as much as possible, it is preferably 0.75 or more and 1.20 or less.

The load ratio (F _70% ) / (F _20% ) of 70% strain load F _70% and 20% strain load F _20% based on the dynamic compression test is an index of shock absorption characteristics and is close to 1. This means that the energy absorption performance is such that the maximum load generated is suppressed as much as possible to absorb a large amount of energy. In the present invention, the load at 70% strain (F _70% ) and the load at 20% strain (F _20% ) based on the dynamic compression test are determined as follows.

  The dynamic compression test is performed according to JIS-K7134. The tester uses a vertical drop tester with a guide, and the shape of the test sample is 100 mm long x 100 mm wide x 50 mm thick, and is tested for 24 hours in a constant temperature room at 23 ± 2 ° C and 50 ± 10% humidity. Sample for use.

  The dynamic compression test is performed in a constant temperature room at 23 ± 2 ° C. and humidity 50 ± 10%. The fall height and the weight of the cone are determined so that the strain of the test sample is 80% or more. A heavy cone is freely dropped on the test sample, and an acceleration a generated in the heavy cone is measured by an accelerometer attached to the heavy cone of the test apparatus, and recorded as a time function.

The load F [kN] is given by the following equation as the product of the acceleration a [G] and the heavy cone mass M [kg].
F [kN] = (a × M × 9.8) / 1000

The height of the heavy cone H is measured while the test sample is compressed by the heavy cone and is recorded as a function of time. The deformation amount of the sample is the difference between the height of the heavy cone H0 and H when the lower surface of the heavy cone and the upper surface of the sample are in contact (deformation amount [mm] = H0−H), and the deformation amount is divided by the initial thickness of the sample. The percentage is the strain.
Strain [%] = (deformation amount / initial thickness of test sample) × 100

As described above, a load at 70% strain (F _70% ) and a load at 20% strain (F _20% ) can be obtained. The load ratio is calculated from these values according to the following formula.
Load ratio = (F _70% ) / (F _20% )

  Moreover, the volume increase rate when the thermoplastic resin foam of this invention is immersed in water for 24 hours is 5% or less. If the volume increase rate is larger than 5%, when the resin foam is used for the bumper core, the bumper face may be deformed when the vehicle body is covered with water. The volume increase rate is calculated by measuring the dimensions of each side of the resin foam cut into a cubic shape, then calculating the volume, then immersing the resin foam in water for 24 hours and measuring the dimensions of each side in the same manner. And the volume increase is divided by the original volume of the resin foam.

  As the thermoplastic resin constituting the thermoplastic resin foam in the present invention, specifically, a polyethylene naphthalate resin, a polycarbonate resin, a polyether ether ketone resin, a phenylene ether resin, and the resin and styrene resin A mixture of resins is mentioned. Further, a copolymer of the monomer constituting the resin with maleic anhydride, N-alkyl substituted maleimide, etc., a copolymer of aromatic vinyl with maleic anhydride, N-alkyl substituted maleimide, etc., aromatic vinyl -Vinyl cyanide copolymer and resin compositions comprising these resins. Among these, a thermoplastic resin composition obtained by mixing a copolymer composed of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide and an aromatic vinyl-vinyl cyanide copolymer is preferable. Among such thermoplastic resins, a thermoplastic resin having a bending fracture strain of 0.1% to 2.5% is preferable.

  These thermoplastic resins preferably have heat resistance. As for the heat resistance of the thermoplastic resin foam of the present invention, the rate of change in the heating dimension when exposed to a hot air circulating dryer maintained at 100 ° C. for 168 hours is preferably 3% or less, and the hot air circulation maintained at 120 ° C. More preferably, the heating dimensional change when exposed to the dryer for 168 hours is 3% or less.

  The cell anisotropy ratio of the thermoplastic resin foam of the present invention is preferably 1.1 or more and 3.0 or less. The cell anisotropy ratio is defined by (cell vertical width) / (cell horizontal width). In the present invention, the compression direction of the foam is the vertical direction, and the direction orthogonal to the vertical direction is the horizontal direction. That is, when the cell is compressed in the longitudinal direction, good energy characteristics can be exhibited. When the vertical direction is determined, there are a plurality of horizontal directions perpendicular to the vertical direction, the cell horizontal width differs depending on which horizontal direction the width is taken, and the anisotropy ratio may be different. In such a case, the anisotropy ratio is calculated by adopting the width in the direction in which the lateral width becomes the smallest.

  When a thermoplastic resin having a bending fracture strain of 0.1% or more and 2.5% or less is subjected to bending deformation, it tends to break while the deformation is small. In addition, a foam having a vertically long shape with a cell anisotropy ratio of 1.1 or more and 3.0 or less tends to cause cell destruction. When compressive deformation is applied to such a foam, a fracture zone on the surface perpendicular to the compression direction is generated, and as the compressive strain is increased, the failure zone is sequentially generated. It is considered that it exhibits excellent energy absorption characteristics.

  The thermoplastic resin foam of the present invention comprises a copolymer (A) 80 to 30% by weight of an aromatic vinyl, an unsaturated dicarboxylic acid anhydride and an N-alkyl-substituted maleimide, and an aromatic vinyl-vinyl cyanide copolymer. (B) It is preferable that the thermoplastic resin composition obtained by mixing 20 to 70% by weight is foamed.

  Examples of the aromatic vinyl constituting the copolymer (A) composed of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl-substituted maleimide include styrene, α-methylstyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, bromo Examples include styrene, chlorostyrene, vinyl toluene, vinyl xylene and the like.

  Of these, styrene and α-methylstyrene are preferred from the viewpoints of compatibility with the aromatic vinyl-vinyl cyanide copolymer (B) and ease of polymerization. Is optimal.

  Examples of the unsaturated dicarboxylic acid anhydride include maleic anhydride, itaconic anhydride, citraconic anhydride, etc. From the viewpoints of compatibility with the copolymer (B), ease of polymerization, and low cost, Is preferred.

  Examples of the N-alkyl-substituted maleimide include N-methylmaleimide, N-butylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-4-diphenylmaleimide, N-2-chlorophenylmaleimide, N-4-bromophenylmaleimide, N-1-naphthylmaleimide and the like are mentioned, and N-phenylmaleimide is most suitable from the viewpoint of compatibility with the copolymer (B), ease of polymerization, and low cost.

  In the copolymer (A) consisting of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl substituted maleimide, the total amount of monomers of aromatic vinyl, unsaturated dicarboxylic acid anhydride and N-alkyl substituted maleimide is When the amount is 100% by weight, the N-alkyl-substituted maleimide is preferably 40% by weight or more from the viewpoint of imparting heat resistance, and in consideration of water absorption and moisture absorption resistance, the unsaturated dicarboxylic acid anhydride is 5% or less. It is preferable that

  Moreover, the copolymer (B) used by this invention consists of aromatic vinyl and vinyl cyanide. As the aromatic vinyl, as described above, styrene and α-methylstyrene are preferable from the viewpoint of compatibility with the copolymer (A) and ease of polymerization, and styrene which is inexpensive in price is used. Is optimal.

  Examples of vinyl cyanide include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile and the like, and acrylonitrile is preferred from the viewpoint of compatibility with the copolymer (A) and ease of polymerization. In view of compatibility with the copolymer (A), ease of polymerization, and low cost, a copolymer of styrene and acrylonitrile is preferred.

  The thermoplastic resin composition in the present invention is obtained by mixing the copolymer (A) and the copolymer (B).

  The weight ratio of the copolymer (A) and the copolymer (B) in the resin composition is preferably 30 to 80% by weight of the copolymer (A) and 70 to 20% by weight of the copolymer (B). More preferably, the copolymer (A) is 35 to 70% by weight and the copolymer (B) is 65 to 30% by weight, the copolymer (A) is 40 to 65% by weight and the copolymer (B) is More preferably, it is 60 to 35% by weight.

  In the present invention, additives such as a nucleating agent, a stabilizer, a lubricant, a flame retardant, an antistatic agent, a plasticizer, a water absorbing agent, and a radiation inhibitor are blended in the thermoplastic resin composition as necessary. May be.

  The thermoplastic resin foam of the present invention can be obtained by a known foaming method.

  As the foaming method for obtaining the thermoplastic resin foam of the present invention, the thermoplastic resin is melt-kneaded in an extruder, and a foaming agent is further injected and kneaded, and extruded from the die into the atmosphere to obtain a foamed molded product. There is a foam molding method.

  In the case of the extrusion foam molding method, when a slit-shaped die is used to form a plate-like extruded foam, the cell anisotropy expands in the thickness direction when the resin is extruded. Foams with a ratio greater than 1.1 can be obtained. In order to significantly increase the cell anisotropy ratio in the thickness direction, the thickness expansion rate when foaming the molten resin into the atmosphere during extrusion foaming is increased. As a method of increasing the thickness enlargement ratio, a slit-shaped die is used as a die, a method of increasing the back pressure during extrusion by reducing the slit thickness, a method of increasing elasticity at the time of melting the resin, or a die flow path For example, there is a method of increasing the die swell by changing. Alternatively, there is a method of increasing the molding resistance during molding. In order to increase the molding resistance, there are a method of reducing the speed of the molding roll, a method of increasing the frictional resistance between the molding die and the foam, and the like.

  Also, a method or resin particle in which foamable resin particles impregnated with a foaming agent are prepared, the foamable resin particles are heated to be prefoamed to produce prefoamed particles, and the prefoamed particles are subjected to in-mold foam molding. In a pressure vessel, an aqueous dispersion containing a dispersant, a surfactant, and a volatile foaming agent are charged. After the temperature is raised and the resin particles are impregnated with the foaming agent, the pre-expanded particles are discharged under a low-pressure atmosphere. There is a bead method in-mold molding method such as a method of preparing and molding the pre-expanded particles in a mold.

  In the in-mold molding method of beads, the method for adjusting the cell anisotropy ratio to a desired range is to fill the pre-expanded particles in a mold, heat and fuse the pre-expanded particles together and expand them. Once a foam with no gaps between particles is formed, one mold is moved, and the foam is further expanded in that direction to obtain a molded body in which the cell shape extends long in the moving direction. it can.

  As a foaming agent for obtaining the thermoplastic resin foam of the present invention, one kind selected from the group consisting of a physical foaming agent and a chemical foaming agent, or a mixture of two or more kinds can be used.

  Specific examples of the physical foaming agent include, for example, hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, neopentane, and cyclopentane; 1,1-difluoroethane, 1,2-difluoroethane 1,1,1-trifluoroethane, 1,1,2-trifluoroethane, 1,1,1,2-tetrafluoroethane, 1,1,2,2-tetrafluoroethane, 1,1,1 , 2,2-pentafluoroethane, difluoromethane, trifluoromethane and other fluorinated hydrocarbons; carbon dioxide, nitrogen, water, argon, helium and other inorganic gases; dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n- And ethers such as butyl ether and diisoamyl ether. These can be used alone or in admixture of two or more.

  Specific examples of the chemical foaming agent include, for example, N, N′-dinitrosopentamethylenetetramine, p, p′-oxybis-benzenesulfonylhydrazide, hydrazodicarbonamide, sodium carbonate, azodicarbonamide, terephthalazide, 5 -Phenyltetrazole, p-toluenesulfonyl semicarbazide and the like. These can be used alone or in admixture of two or more.

The density of the thermoplastic resin foam of the present invention is preferably 11 kg / m ³ or more and 110 kg / m ³ or less from the viewpoint that good energy absorption characteristics can be obtained. The density can be adjusted.

  The foamed molded article obtained by the molding method of the present invention is suitably used for automobile side impact pads, bumper core materials (cores) and the like.

  Hereinafter, although the thermoplastic resin foam of this invention is demonstrated in detail by a specific Example, this invention is not limited only to this Example. In the following, “part” and “%” are based on weight unless otherwise specified.

(Test method)
[Dynamic compression test]
The resin foam is cut into a rectangular parallelepiped shape with a length of 100 mm, a width of 100 mm, and a thickness of 50 mm so as not to include the surface skin layer, and left in a constant temperature room at a temperature of 23 ° C. ± 2 ° C. and a humidity of 50 ± 10% for 24 hours. It was set as the test piece for a compression test.

  The dynamic compression test was carried out in a temperature-controlled room at a temperature of 23 ± 2 ° C. and a humidity of 50 ± 10% using a shock impact tester CST-320S for shock absorbers manufactured by Yoshida Seiki Co., Ltd. The energy given to the test piece in the dynamic compression test is determined by the product of the drop height and the weight of the heavy cone. The drop height and the weight of the cone in the present invention were determined so that the strain of the evaluation sample was 80% or more.

An acceleration converter AS-500HA manufactured by Kyowa Denki Co., Ltd. was fixed to the heavy cone of the test machine, and the acceleration G applied to the heavy frustum was measured. The load F [N] generated by the impact is given by the following equation as the product of the acceleration a [G] and the heavy cone weight M [kg].
F [kN] = (a × M × 9.8) / 1000

The deformation amount of the evaluation specimen was measured using a laser displacement meter manufactured by Keyence Corporation. The displacement meter is attached to the testing machine, and a distance H between the displacement meter and the displacement meter is measured. The method of calculating the deformation amount of the evaluation test piece is calculated from the distance H0 at the time when the output of the accelerometer is obtained out of the measured distance, that is, when the dropping jig and the evaluation test piece are in contact by the following equation.
Deformation amount [mm] = H0−H

The strain based on the dynamic compression test is expressed as a percentage by dividing the amount of deformation by the thickness of the test piece as represented by the following equation.
Strain [%] = (Deformation amount / Evaluation sample thickness) × 100

The load F _70% at the time of 70% strain and the load F _20% at the time of 20% strain based on the dynamic compression test are defined by the load measured at the time of the strain when the strain is defined as described above. . The load ratio was calculated from these values according to the following formula.
Load ratio = (F _70% ) / (F _20% )

[Bending fracture strain]
The measurement of bending fracture strain is performed according to JIS-K7171. The foam base resin was molded into a strip-shaped test piece having a thickness of 6 mm, a width of 15 mm, and a length of 120 mm, and left for 24 hours in a thermostatic chamber at 23 ° C. ± 1 ° C. to obtain a test piece for a bending test. A three-point bending test was performed using a tensile compression tester manufactured by Minebea Co., Ltd. The distance between fulcrums was 90 mm, and the test speed (indenter descending speed) was 2 mm / min. The breaking strain ε _b [%] is given by the following equation from the deflection s _b [mm] at break, the thickness h [mm] of the test piece, and the distance L [mm] between fulcrums.
ε _b = (6 × h × s _b × 100) / (L ² )

[Cell anisotropy ratio]
A line was drawn in each of the vertical and horizontal directions of the foam cross-sectional photograph, the number of cells crossing the line was counted, and the width per cell was calculated by dividing the length of the line by the number of cells. The cell anisotropy ratio was calculated according to the following formula. The foam thickness direction was vertical and the direction perpendicular thereto was horizontal.
Cell anisotropy ratio = (cell vertical width) / (cell horizontal width)

[Volume change test by water absorption]
A resin foam is cut out into a cube shape of 25 mm in length, 25 mm in width, and 25 mm in height so as not to include the surface skin layer, and left for 24 hours in a temperature-controlled room at 23 ° C. ± 1 ° C. to obtain a test piece for volume change measurement. It was. The length, width, and height of the test piece were measured, and the volume V _{1 of the} test piece was calculated from the following formula.
V ₁ = vertical x horizontal x height

The test after the resin foam is completely immersed in water and the length, width and height of the test piece are measured for 24 hours in a constant temperature room at 23 ° C. ± 1 ° C. The volume of the piece was calculated.
V ₂ = Vertical x Horizontal x Height

The volume increase rate was calculated by the following formula.
Volume increase rate [%] = {(V ₂ −V ₁ ) / V ₁ } × 100

[Heat resistance test]
The heating dimensional change rate was measured according to JIS-K6767. On a foamed molded product on a flat plate of length 100mm, width 100mm, and thickness 25mm, three straight lines that are parallel to each other in the vertical and horizontal directions are entered at equal intervals of 33.3mm. The dimension was measured and it was set as the dimension (L1) before a heating. Next, the foam was placed horizontally in a hot air circulating drier kept at 120 ° C., heated for 168 hours, then taken out, measured for the dimensions of the sample, and defined as the dimension after heating (L2). The heating dimensional change rate was calculated from the following equation.
Heating dimensional change rate (%) = ((L2−L1) / L1) × 100
Moreover, the same test was done by setting the temperature of the hot air circulating dryer to 100 ° C., and the heating dimensional change rate at 100 ° C. was calculated by the same formula.

Example 1
Copolymer (A) as a copolymer of 49% styrene, 50% N-phenylmaleimide, and 1% maleic anhydride, manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: DENKA IP MS-NA, copolymer ( As B), AS-XGS manufactured by Denki Kagaku Kogyo Co., Ltd., which is a copolymer of acrylonitrile 25% and styrene 75%, was used, and the copolymer (A) / copolymer (B) was 80% / 20%. The thermoplastic resin composition was mixed at a ratio of As a result of molding the thermoplastic resin composition and conducting a bending test, the bending breaking strain was 0.32%.

  To 100 parts of this resin composition, 0.5 part of talc (trade name: Talcan powder, manufactured by Hayashi Kasei Co., Ltd.) is dry blended as a nucleating agent, and the resulting resin composition is a single stage having a diameter of 65 mm. This was fed at a rate of 50 kg / hour to a two-stage connection type extruder in which a first-stage extruder and a second-stage extruder having a diameter of 90 mm were connected in series. The resin composition supplied to the extruder having a diameter of 65 mm was melted and kneaded by heating to about 280 ° C., and then 2.5 parts of dimethyl ether and 3.5 parts of n-butane were used as blowing agents near the tip of the first stage extruder. The part was pressed into the molten thermoplastic resin composition.

Thereafter, the resin is cooled so that the resin temperature becomes 200 ° C. with an extruder having a diameter of 90 mm connected thereto, and extruded from the die lip of a rectangular slit die provided at the tip of the extruder having a diameter of 90 mm to a density of 42 kg / An extruded foam of cm ³ was obtained. Table 1 shows the anisotropy ratio of the cells calculated by observing the cell structure of the foam obtained by a microscope. The resulting foam was subjected to a dynamic compression test, and the calculated load ratio = (F _70% ) / (F _20% ) is shown in Table 1. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C.

(Example 2)
The mixing ratio of copolymer (A) / copolymer (B) was changed to 60% / 40%, and the heating and kneading temperature in an extruder with a diameter of 65 mm was 260 ° C., and cooling with an extruder at a diameter of 90 mm. Extruded foam having a density of 39 kg / cm ³ was obtained under the same conditions as in Example 1 except that the temperature was changed to 180 ° C. Table 1 shows the anisotropy ratio of the cells calculated by observing the cell structure of the foam obtained by a microscope. The resulting foam was subjected to a dynamic compression test, and the calculated load ratio = (F _70% ) / (F _20% ) is shown in Table 1. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C. The thermoplastic resin composition used in Example 2 (copolymer (A) / copolymer (B) mixing ratio: 60% / 40%) was molded and subjected to a bending test. The strain was 0.49%.

(Example 3)
The mixing ratio of copolymer (A) / copolymer (B) was changed to 30% / 70%, and the heating and kneading temperature in an extruder with a diameter of 65 mm was 240 ° C., and cooling with an extruder at a diameter of 90 mm. Extruded foam having a density of 28 kg / cm ³ was obtained under the same conditions as in Example 1 except that the temperature was changed to 140 ° C. Table 1 shows the anisotropy ratio of the cells calculated by observing the cell structure of the foam obtained by a microscope. The resulting foam was subjected to a dynamic compression test, and the calculated load ratio = (F _70% ) / (F _20% ) is shown in Table 1. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C. The thermoplastic resin composition used in Example 3 (copolymer (A) / copolymer (B) mixing ratio was 30% / 70%) was molded and subjected to a bending test. The strain was 0.74%.

Example 4
PS Japan Co., Ltd., polystyrene G9401, the same conditions as in Example 1 except that the heating and kneading temperature in an extruder with a diameter of 65 mm was changed to 200 ° C. and the cooling temperature in an extruder with a diameter of 90 mm was changed to 120 ° C. To obtain an extruded foam having a density of 31 kg / cm ³ . Table 1 shows the anisotropy ratio of the cells calculated by observing the cell structure of the foam obtained by a microscope. The resulting foam was subjected to a dynamic compression test, and the calculated load ratio = (F _70% ) / (F _20% ) is shown in Table 1. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C. In addition, as a result of shaping | molding the thermoplastic resin (PS Japan Co., Ltd. product, polystyrene G9401) used in Example 4, and performing the bending test, the bending fracture | rupture distortion was 0.92%.

(Comparative Example 1)
A test piece was cut so that the extruded foam obtained by the same method as in Example 1 was compressed in the extrusion direction, that is, the direction orthogonal to the thickness direction, and a dynamic compression test was performed. The cell anisotropy ratio was calculated with the extrusion direction as the longitudinal direction. The results are shown in Table 1. The resulting foam was subjected to a dynamic compression test, and the calculated load ratio = (F _70% ) / (F _20% ) is shown in Table 1. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C. In addition, as a result of shaping | molding the thermoplastic resin composition used by the comparative example 1 and implementing the bending test, the bending fracture | rupture distortion was 0.49%.

(Comparative Example 2)
100 parts by weight of the thermoplastic resin composition obtained by the same method as in Example 2 was supplied to a single screw extruder and melt kneaded to obtain 0.8 mg of resin particles per grain.

  A 6 L autoclave equipped with a stirrer was charged with 100 parts of the obtained thermoplastic resin particles, 100 parts of water, 0.2 part of calcium phosphate, and 0.006 part of an α-olefin sulfonate. Next, 10 parts of normal butane was added, the temperature was raised to 125 ° C. while stirring, and the temperature was maintained for 9.5 hours to impregnate the thermoplastic resin particles with a foaming agent to obtain expandable thermoplastic resin particles. .

The mixture was heated with 190 ° C. steam generated by a heated steam generator for 2 minutes and 40 seconds to obtain pre-expanded particles having a bulk magnification of 25 times. The obtained pre-expanded particles were filled in a mold having a length of 450 mm × width of 350 mm × thickness of 40 mm, molded by heating with 0.38 MPa steam for 10 seconds, and cooled to a density of 45 kg / m ^3. The foamed molded product was obtained. Table 1 shows the anisotropy ratio of the cells calculated by observing the cell structure of the obtained foam with a microscope. The resulting foam was subjected to a dynamic compression test, and the calculated load ratio = (F _70% ) / (F _20% ) is shown in Table 1. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C. In addition, as a result of shaping | molding the thermoplastic resin composition used by the comparative example 2 and implementing the bending test, the bending fracture | rupture distortion was 0.49%.

(Comparative Example 3)
A dynamic compression test was performed on a rigid polyurethane foam having a density of 58 kg / cm ^{3 using} diphenylmethane-4,4′-diisocyanate and polypropylene glycol as raw materials, and the calculated load ratio = (F _70% ) / (F _20% ) Table 1 shows. Table 1 shows the anisotropy ratio of the cells calculated by observing the cell structure of the foam obtained by a microscope. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C.

(Comparative Example 4)
A dynamic compression test was performed on a rigid polyurethane foam having a density of 79 kg / cm ^{3 using} diphenylmethane-4,4′-diisocyanate and polypropylene glycol as raw materials, and the calculated load ratio = (F _70% ) / (F _20% ) Table 1 shows. Table 1 shows the anisotropy ratio of the cells calculated by observing the cell structure of the foam obtained by a microscope. Furthermore, Table 1 shows the measurement results of the volume change rate when the obtained foam was immersed in water and the heating dimensional change rate at 100 ° C and 120 ° C.

Claims (10)

The load ratio (F _70% ) / (F _20% ) between the load at 70% strain (F _70% ) and the load at 20% strain (F _20% ) based on the dynamic compression test is 0.70 or more and 1 Thermoplastic resin foam having a volume increase rate of 5% or less when immersed in water for 24 hours.   The thermoplastic resin foam according to claim 1, wherein the cell-shaped anisotropy ratio is 1.1 or more and 3.0 or less.   80-80% by weight of copolymer (A) composed of aromatic vinyl, unsaturated dicarboxylic anhydride and N-alkyl-substituted maleimide and 20-70% by weight of aromatic vinyl-vinyl cyanide copolymer (B) are mixed The thermoplastic resin foam according to claim 1 or 2, wherein the thermoplastic resin composition is foamed.   The thermoplastic resin foam according to claim 3, wherein the aromatic vinyl is styrene.   The thermoplastic resin foam according to claim 3, wherein the unsaturated dicarboxylic acid anhydride is maleic anhydride.   The thermoplastic resin foam according to claim 3, wherein the N-alkyl-substituted maleimide is N-phenylmaleimide.   The thermoplastic resin foam according to claim 3, wherein the vinyl cyanide is acrylonitrile.   The thermoplastic resin foam according to any one of claims 1 to 7, wherein the thermoplastic resin foam is produced by an extrusion foam molding method.   The bumper core for motor vehicles which consists of a thermoplastic resin foam as described in any one of Claims 1-8.   An automobile side bump pad comprising the thermoplastic resin foam according to any one of claims 1 to 8.