JPH09136331A - Method for in-mold molding of thermoplastic resin foam molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a foam molding with good appearance and sufficiently performed welding by only one filling when a molded item with different densities is manufactured by means of one molding machine by filling foaming particles each with a different inner pressure are simultaneously filled in a mold through independent filling holes. SOLUTION: When molding is performed by filling foaming particles by compression filling, even if the filling condition is the same, the foaming particles with a low inner pressure generate remarkable shrinkage by the outer pressure during filling (in a method for compression filling, as the pressures in a raw material feeding tank 7' and a mold 4 is elevated at least to an atmospheric pressure, the outer pressure acts on the foaming particles). Therefore, the compression ratio becomes high by filling to obtain a molded article with a high density. On the other hand, as the foaming particles with a high inner pressure has a small pressure difference to the outer pressure during filling, filling is performed by a low compression ratio to obtain a molded article with a low density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for in-mold molding of thermoplastic resin foam moldings having different densities. More specifically, for example, even when foamed particles having the same bulk density are used, the number of molding steps is increased. Without increasing the appearance, good appearance, fusion was also sufficiently performed, relates to a molding method to obtain a foamed molded product having a different density, various molded products obtained by the present invention,
It is used as a cushioning material, heat insulating material, structural member, core material, etc., and is particularly effective for automobile parts.

[0002]

2. Description of the Related Art Expanded particles of thermoplastic resin such as polystyrene, polyethylene, polypropylene, etc. are filled in a mold, and the expanded particles are fused by heating to form an expanded molded article. This has been done industrially in the past. The foamed molded product thus obtained is widely used as a cushioning material, a heat insulating material and the like due to its excellent physical properties. Since various physical properties of the foamed molded product obtained in this way largely depend on the expansion ratio, when used as a cushioning material, consider the allowable acceleration of the portion requiring cushioning, the design collision speed, the shape, etc. Then, the magnification and dimensions of the foamed molded product are designed.

For example, when it is used as an impact energy absorbing material as a bumper core material, it is divided into a front bumper and a rear bumper. However, as a result of the above design, different expansion ratios may be required. Occur. In such a case, conventionally, one or more front bumper molds were attached to a molding machine, and after molding a required predetermined amount, the mold was replaced with a rear humper mold, The method of molding the foamed molded body of the rear bumper core material has been carried out again.

On the other hand, even if the same molded product is used, it is sometimes required that the magnification be different for each part in view of the required physical properties. For example, when a foamed molded product is used as a bumper core material, the foamed product is designed to absorb energy from the outside when the foamed product is distorted by a predetermined width when a shock is applied from the front. Since there is a case where the part having the part of (2) has cracks or scratches when it is distorted, it is sometimes desired that the density be different from that of the central part so as to keep the amount of distortion low.

As a method for producing these, there is a method in which each of them is preliminarily molded at a required magnification to form a foamed molded article, and then the foamed molded article is integrated by adhesion or the like.
In this method, there is a problem that it takes time and effort to integrate the respective parts, and many molds corresponding to the parts are required, resulting in high mold manufacturing cost and complicated process control.

Further, in the method of filling and foam-molding in one mold by using two or more kinds of expanded particles having originally different densities, the expanded particles of high bulk density are simultaneously obtained under the filling conditions of expanded particles of low bulk density. In this case, the expanded particles having a high bulk density are filled at a low compression rate, so that only molded products having a poor appearance with many interparticle voids can be obtained. On the contrary, under the filling conditions of expanded particles of high bulk density, expanded particles of low bulk density are excessively filled into the mold, so that steam does not sufficiently reach the inside of the mold and fusion of the molded product is poor. Therefore, it is necessary to set conditions suitable for each foamed particle in the filling step, and there is a disadvantage in that the filling step must be performed a plurality of times.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that when molding products having different densities with a single molding machine, particles having different internal pressures are used. It was found that, by using the foamed product once, it is possible to obtain a foamed molded product having a good appearance and sufficient fusion bonding, thereby completing the present invention. That is, the present invention is a method of filling a thermoplastic resin foamed particle in a mold and molding the foamed particle by heating to fuse the foamed particles to each other to form a foamed molded article, in which the foamed particles have a plurality of two or more different internal pressures. An in-mold molding method for a thermoplastic resin foam-molded article, which is composed of foamed particles and is filled into the mold at the same time through separate filling ports. In addition, the differential scanning calorimeter of the base resin of a plurality of foamed particles of two or more
The difference in melting peak temperature obtained when the temperature is raised at a rate of 0 ° C./minute is preferably within 15 ° C.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, it is necessary to use two or more kinds of expanded particles having different internal pressures, whereby molded articles having different densities can be obtained even with expanded particles having the same bulk density. is there. That is, expanded particles having a low internal pressure are packed at a high compression rate, and expanded particles having a high internal pressure are packed at a low compression rate, so that expanded particles having the same bulk density can have different densities, sizes, and appearances. A molded product can be obtained. For example, in the case of filling foamed particles by compression filling and molding, even under the same filling conditions, the foamed particles with a low internal pressure will have a large external pressure at the time of filling (in the compression filling method, the inside of the raw material supply tank and the mold will be large. Since the pressure is increased to atmospheric pressure or more, an external pressure acts on the expanded particles), and a considerable shrinkage occurs. Therefore, the compression rate becomes high due to the filling, and thus a molded product having a high density is obtained.
On the other hand, the expanded particles with high internal pressure are
Since the differential pressure is small, it will be filled at a low compression rate,
Therefore, the molded product has a low density.

[0009] For example, more detailed description will be made with reference to an example using expanded particles having an internal pressure of atmospheric pressure and expanded particles having an internal pressure increased to 0.5 kg / cm ² G or more. In the former particles, if the bulk density is 0.1 to 0.01 g / cm ³ , the compressibility is 10 to 6 at a filling chamber pressure of 0.5 to 5 kg / cm ² G.
It will be filled at about 0%.

On the other hand, in the latter expanded particles, the internal pressure acts as a force against the chamber pressure, which is the external pressure of the expanded particles, so that the compression rate is as low as 0 to 40% under the same conditions. Therefore, in the former particles filled with a high compressibility, a restoring force against compression works as a force to fill the gaps between the expanded particles, and at the same time, the secondary expansion force of the expanded particles themselves contributes to It is possible to obtain a high-density molded product having a mold-like density. On the other hand, in the latter particles filled with a low compressibility, the expansion force due to the pressure inside the expanded particles and the secondary expansion force of the expanded particles themselves contribute as a force to fill the gap between the expanded particles,
It is possible to obtain a molded product having a low density as a mold.
As described above, in any of the molds, there is a difference in the mechanism for filling the gap between the foamed particles in the molding, the dimension imprinted according to the mold and the gap between the foamed particles are filled, the appearance is excellent, and the fusion is good. A simple molded product can be made with only one filling step.

In the present invention, the internal pressure of the expanded particles can be applied by a known method. If the density and compression rate required for the molded product are determined, the required bulk density and the internal pressure of the foamed particles are determined, so that an optimum internal pressure applying means may be implemented. The internal pressure applying means is, for example, Japanese Patent Publication No.
2951, JP 61-40334 A, JP 1-2
75104, JP 58-101025 A, JP 6
As described in each publication such as 0-24933, foamed particles are placed in a pressure resistant container, and an inorganic gas such as nitrogen, air, carbon dioxide, or a low boiling point hydrocarbon such as propane, butane, dichlorodifluoromethane, etc. And halogenated hydrocarbons 1
It can be carried out by impregnating the inside of the particles under pressure with two or more kinds.

As the thermoplastic resin constituting the expanded particles in the present invention, polystyrene resin, polyethylene resin, polypropylene resin and the like are used, and among them, polyolefin resin expanded particles such as polyethylene or polypropylene resin are preferable. .

In the present invention, after the filling, a heating medium such as steam is introduced into the mold to fuse the foamed particles together,
Since a foamed molded product is obtained, it is desirable that the melting peak temperatures of the resins, which are the raw materials of the plurality of foamed particles of two or more types, are close to each other, because the fusion is sufficiently performed. Particularly preferably, the difference in melting peak temperature is within 15 ° C, and more preferably within 10 ° C.

If the temperature difference is large, when the resin is heated at a heating temperature suitable for the expanded particles of the resin having a low melting peak temperature, the expanded particles of the resin having a high melting peak temperature are insufficiently heated to cause poor fusion. On the other hand, when heated at a heating temperature suitable for foamed particles of resin having a high melting peak temperature, foamed particles of resin having a low melting peak temperature become overheated, the molded product is in a melted state, and the size significantly shrinks. Or deformation may occur, which is not preferable. From the above, in the present invention, it is most preferable to use the expanded particles having the same melting peak of the raw material resin. In the present invention, the melting peak temperature of the raw material resin is measured by a differential scanning calorimeter in accordance with the method of JIS K7121 to a test amount of about 5 mg per minute.
In the curve recorded when heated at 0 ° C., the temperature of the endothermic peak generated during crystal melting of the sample resin is shown.

In the present invention, the method for producing expanded particles is not particularly limited, and a conventionally known method, that is, any method can be used. For example, a method in which resin particles containing a decomposable foaming agent are heated to a temperature equal to or higher than the decomposition temperature of the foaming agent to foam, or resin particles impregnated with a volatile foaming agent are heated and heated by an external heat source such as steam to foam. Method, a method of discharging resin particles impregnated with a volatile foaming agent from a high-temperature and high-pressure atmosphere under a low pressure to foam.
Any method may be used, such as a method in which a resin obtained by melt-kneading a foaming agent with an extruder is extruded from a die having pores and foamed, and then cut.

The expanded beads thus obtained are filled by a conventional appropriate filling method such as compression filling, cracking filling, etc. and heated to form a foamed molded article. The molding method of the present invention uses one molding machine as shown in FIG. 1 in which a plurality of molds are present and the molding conditions such as heating are the same to obtain moldings having different densities. As shown in FIG. 2, the present invention can be applied to the case where it is desired to obtain a molded product having a portion having different densities in one molded product. Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples as long as the scope of the claims is not exceeded.

[0017]

【Example】

 Example 1 This example was carried out using the apparatus whose outline is shown in FIG.
As a raw material 1, an internal temperature of 50 ° C. and an initial pressure of 1.
0kg / cm^Two・ Pressurize with G and after 4 hours 3.0 kg /
cm^Two・ 0.5kg / cm to become G^TwoBoosted at
While applying pressure, the internal pressure is 1.8 kg / cm
^Two・ Ethylene propionate with a bulk density of 30g / l given to G
Ren random copolymer (ethylene content 2.6% by weight, melt
With expanded particles having a solution peak temperature of 144 ° C) and as raw material 2
Pressure 0kg / cm^Two-G ethylene with a bulk density of 30 g / l-
Propylene random copolymer (ethylene content 2.6 wt
%, Melting peak temperature 144 ° C.)
Put it in the raw material storage tank 7, 7 '
3.0 kg / cm inside the tank ^Two・ Compressed to G
I applied pressure. While maintaining the pressure of the raw material storage tank
2.5 kg / cm^Two・ Gold pressed to G
The mold cavities 3 and 4 were filled with the respective foamed particles.
At this time, the pressure of 3 and 4 is 2.5 kg / cm^Two・ Hold to G
I was 3.5k after setting the pressure in the cavity to atmospheric pressure
g / cm^Two・ Introduce G vapor to fuse particles together
Was. Subsequently, water cooling and air cooling are performed, and the surface pressure of the molded product becomes 0.
5 kg / cm^Two・ Open the mold when it reaches G,
The molded product of No. 4 was taken out. The molded product of 3 has a density of 37.5.
g / l (compressibility 20%) with no gap between particles
It was a view. The molding gap of 4 also has a density of 60 g / l (pressure
50%) and good appearance with no gaps between particles,
Different density from one molding machine without increasing the number of molding processes
A molded product of was obtained.

Example 2 This example was carried out using the apparatus whose outline is shown in FIG.
In the same manner as in Example 1, foamed particles composed of an ethylene / propylene random copolymer having an internal pressure of 1.8 kg / cm ² · G and a bulk density of 30 g / l, and an internal pressure of 0 kg / cm ² · G having a bulk density of 30 g / l Foamed particles made of ethylene / propylene random copolymer were put in the raw material storage tanks 7, 7 ', respectively, and the inside of the tank was compressed with compressed air to 3.0 kg / cm ² ·.
Pressurized to G. Each of the mold cavities 3'and 4'which were cut off by the partition wall 8 was filled with respective foamed particles while being pressurized to 2.5 kg / cm ² · G. After the completion of filling, the wall-operated cylinder 9 was used to remove the threshold value of 8, followed by heating with steam of 3.5 kg / cm ² · G, followed by water cooling and air cooling for molding. The molded product thus obtained was well fused and integrated even at the boundary between 3'and 4 ', and the densities of 3'and 4'differences of 37.5 g / l and 60 g / l were different. The density was good, and there was no interparticle gap in either part, which was good.

Comparative Example 1 The raw materials to be put in the raw material storage tanks 7 and 7'are ethylene / propylene random copolymers (ethylene content 2.6% by weight, internal pressure 0 kg / cm ² · G, bulk density 30 g / l). Molding was performed in the same manner as in Example 1 except that expanded particles having a melting peak temperature of 144 ° C.) were used. The molded products of Nos. 3 and 4 had the same density at 60 g / l (compression rate 50%).

Comparative Example 2 In the raw material storage tank 7, an ethylene / propylene random copolymer having an internal pressure of 0 kg / cm ² · G and a bulk density of 15 g / l (ethylene content 2.6% by weight, melting peak temperature 144
℃) foamed particles, and 7'internal pressure 0kg / c
Same as Example 1 except that the foamed particles made of ethylene / propylene random copolymer (ethylene content 2.6% by weight, melting peak 144 ° C.) having a bulk density of m ² · G of 30 g / l were added and molded. Molded. 4 is 60
At 3 g / l (compressibility of 50%), there was no interparticle gap and good fusion, but the molded product of 3 was 43 g / l (compressibility of 6).
5%), there was no interparticle gap, but the molded article was not fused at all.

Comparative Example 3 The pressure of the raw material storage tanks 7 and 7'was 1.5 kg / cm ² ·.
G and the mold cavities 3 and 4 are 1.0 kg / cm ² ·
Molding was performed in the same manner as Comparative Example 2 except that molding was performed as G. The molded product of 3 was 30 g / l (compression ratio 50%) and had good fusion with no interparticle gap, while the molded product of 4 was 3
At 3 g / l (compressibility 9%), only intergranular gaps and bad appearance were obtained.

Comparative Example 4 In the raw material storage tank 7, linear low-density polyethylene having a bulk density of 47 g / l (density of 0.924 g / ml, melting peak temperature of 123 ° C.) given an internal pressure of 1.2 kg / cm ² · G. )
Foamed particles consisting of, while 7'internal pressure 0 kg / c
m ² · G bulk density 30 g / l ethylene / propylene copolymer (ethylene content 2.6% by weight, melting peak temperature 1
Molding was performed in the same manner as in Example 1 except that expanded particles composed of 44 ° C.) were added. The molded product of No. 4 had a density of 60 g / l (compression rate of 50%) and had good fusion without gaps between particles, while the molded product of No. 3 had a density of 80 g / l (compression ratio of 41%) and had a surface It melted like a keloid and had large shrinkage as a whole.

[0023]

EFFECTS OF THE INVENTION According to the present invention, for example, even if expanded particles having the same bulk density are used, a foamed molded article having a good appearance and a sufficient fusion bonding and different densities can be obtained by a single filling. be able to.

[Brief description of the drawings]

FIG. 1 is an example of a mold used in the molding method of the present invention.

FIG. 2 is another example of the mold used in the molding method of the present invention.

[Explanation of symbols]

 1a, 2b Mold frame 2a, 2b Inside plate 3a, 3b Mold 4a, 4b Mold 5,5 'Filling gun 6,6' Raw material supply line 7,7 'Raw material storage tank 8 Partition wall 9 Wall working cylinder

Claims (2)

[Claims] 1. A thermoplastic resin expanded particle is filled in a mold,
In a method of forming a foamed molded article by fusing foamed particles together by heating, the foamed particles are composed of a plurality of foamed particles of two or more kinds having different internal pressures, and each of them is simultaneously injected into the mold from different filling ports. A method for in-mold molding of a thermoplastic resin foam-molded article, which comprises: 2. A difference in melting peak temperature obtained when the temperature is raised at a rate of 10 ° C./min with a differential scanning calorimeter of the base resin of the plurality of foamed particles of two or more kinds is within 15 ° C. The in-mold molding method according to claim 1, wherein: