JPH0925356A - Production of noncross-linked preexpanded polyethylene resin particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the production of noncross-linked preexpanded polyethylene resin particles having a specified resin density or higher by impregnating particles of a resin mixture comprising four specific resins with a blowing agent and using a multistep temp. rise method whereby the expansion ratio of the particles is increased stepwise. SOLUTION: Noncross-linked preexpanded polyethylene resin particles are produced by a multistep temp. rise method wherein a resin mixture comprising 30-50wt.% high-pressure low-density PE resin (A) having a density of 0.930-0.980g/cm<3> and an m.p. of 108-118 deg.C, 5-30wt.% linear low-density PE resin (B) having a density of 0.916-0.928g/cm<3> and an m.p. of 118-123 deg.C, 20-45wt.% linear high-density PE resin (C) having a density of 0.955-0.970g/cm<3> and an m.p. of 128-135 deg.C, and 10-35wt.% linear high-density PE resin (D) having a density of 0.940-0.954g/cm<3> and an m.p. in the range of the average m.p. of ingredients B and C ±2 deg.C is impregnated with a blowing agent, expanded under heating to an expansion ratio of 1.5-3.5cc/g, impregnated with a blowing agent to allow it to come into cells of the expanded particles, and further expanded under heating to a higher expansion ratio.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved technique for producing non-crosslinked pre-expanded particles of polyethylene resin. This non-crosslinked pre-expanded particle is a raw material for obtaining a foam-molded article just like a mold cavity by mainly filling it in a mold to heat-expand, and heat-sealing the particles together. Is used as.

[0002]

2. Description of the Related Art Conventionally, a method for producing non-crosslinked pre-expanded particles is known, in which a polyethylene-based resin is used as a raw material resin and the resin particles are impregnated with a foaming agent to expand the resin particles (for example, JP-B-60-10047). No. Gazette, Japanese Patent Publication Sho 60
-10048, JP-A-6-316645,
See JP-A-6-157803).

In this type of technique, when a polyethylene resin is used as a raw material resin, good quality pre-expanded particles cannot be obtained unless the resin is cross-linked and modified, so that a practical foamed molded product cannot be produced. Is to be expanded in a non-crosslinked state so that high-quality pre-expanded particles and expanded molded articles can be obtained. One of the improvements is in the selection of the raw material resin. Specifically, in JP-A-6-316645, a mixed resin of two components of a linear low density polyethylene resin and a linear high density polyethylene resin is disclosed. To adopt
Further, in JP-A-6-157803, 20-85% by weight of high-pressure low-density polyethylene resin, 0-45% by weight of linear low-density polyethylene resin, and 0-40% by weight of linear high-density polyethylene resin. It has been proposed to employ a mixed resin of 2 to 3 components of

Further, the difficulty in foaming the polyethylene resin is that the foaming agent (inorganic gas) impregnated in the particles is severely dissipated at the time of heating for foaming, so that the expected bubble structure /
This is because it is difficult to obtain expanded particles having an expansion ratio and it is difficult to maintain the melt viscosity in a state suitable for foaming because the melt viscosity of the resin has a large temperature dependency. Incidentally, it is said that the temperature range of the non-crosslinked high-pressure low-density polyethylene resin that can maintain the melt viscosity suitable for foaming is at most 1 ° C., and it is difficult to foam because the temperature control is difficult. The proposal to adopt a linear low-density polyethylene resin or a mixed resin with them as the raw material resin is to combine different melting points indicated by different resin (copolymer) components, and to set the appropriate heating temperature range during foaming as a whole. Is intended to be expanded so that expanded particles can be produced in a non-crosslinked state.

On the other hand, there are the following two methods for producing the pre-expanded particles.
Methods are known. That is, the expandable resin particles in a state of being impregnated with a foaming agent are held in an aqueous suspension state in a pressure container, the temperature of the expandable resin particles in the container is adjusted to an appropriate foaming temperature, and the temperature is adjusted from one end of the container. The so-called "flash" in which the expandable resin particles are discharged together with the aqueous suspension liquid under normal temperature and atmospheric pressure to expand the expandable resin particles at a stretch to obtain the expanded particles having a target high expansion ratio in one step. A method called "foaming method" and a method in which resin particles are impregnated with a small amount of a foaming agent in a pressure vessel, once cooled, taken out and transferred to a foaming pot, and the temperature of the foaming pot is raised to an appropriate temperature for foaming. To form expanded particles with a low expansion ratio, and then based on the obtained expanded particles, an inorganic gas is pressed into the bubbles of the expanded particles in a pressure vessel to form expandable expanded particles, which are heated and foamed by heating. Repeat the process of making expanded particles with a higher expansion ratio several times Te, there is a method called a so-called "multi-stage heating foaming method" referred to in the foamed particles of stepwise high expansion ratio. Both of these two foaming methods were developed as improved foaming methods for polyethylene-based resins that are difficult to foam.

However, the "flash foaming method" and the "multi-stage temperature rising foaming method" are used in terms of suppressing the above-mentioned escape phenomenon of the foaming agent in the foaming method and highly adjusting the appropriate range of the heating foaming temperature. For comparison, the "flash foaming method" is the more advantageous method. The reason is that in the "multi-stage temperature rising foaming method", the temperature of the expandable particles used for foaming (expansion) is raised to an appropriate temperature for foaming, and the temperature is raised in an open foaming pot (container). Therefore, the escape of the foaming agent (inorganic gas) cannot be suppressed until the temperature rises, and further, the phenomenon that foaming (expansion) starts before reaching the foaming suitable temperature occurs. Therefore, even though it can be applied to a resin (for example, a crosslinked modified resin) in which the suitable range of the heating foaming temperature (the temperature showing the proper foaming viscosity) at the time of foaming is sufficiently expanded, the suitable range of the foaming temperature is In the case of a narrow high-density linear polyethylene resin having a narrow width, the cell structure is greatly disturbed in the process of foaming (expanding), and it is extremely difficult to form expanded particles in a non-crosslinked state. By the way, when a linear low-density polyethylene resin is adopted, the suitable range of the foaming temperature is somewhat widened by the action of the copolymerization component, so it is possible to form expanded particles by the "multi-stage temperature-rise foaming method". However, even in this case, the foamed particles of these types have a disordered cell structure in the process of foaming, which makes it impossible to obtain a molded product of good quality from the pre-foamed particles.

On the other hand, in the "flash foaming method", the expandable resin particles in the container can be adjusted and maintained in a foaming-appropriate state immediately before the discharge foaming by setting and adjusting the pressure and temperature in the closed container. As a result, even a resin having a relatively narrow foaming suitable temperature (foaming suitable viscosity) range can be easily foamed, and pre-expanded particles having a high expansion ratio of 60 cc / g can be obtained by one-step expansion operation. Moreover, it is easy to obtain a high-quality molded product. The actual state of this process will be further clarified by using the above-mentioned prior document, Japanese Patent Publication No. 60-10047 (and Japanese Patent Publication No. 600048).

Table 5 below shows Japanese Patent Publication No. 60-10047.
The results of additional tests and reference comparative tests of Japanese Patent Publication No. 60-15048 and Japanese Examined Patent Publication No. 60-10048, showing a foaming method at the time of foaming when linear low-density polyethylene and linear high-density polyethylene are used as raw materials It shows another suitability. In this test, both publications do not describe "multi-stage temperature rising foaming method", and the conditions of the molding method and the evaluation method of the molded body are not described in detail. It was tested by supplementing common-sense methods and conditions.

Therefore, when the results of Table 5 are divided into the "flash foaming method" and the "multi-stage temperature rising foaming method", the pre-expanded particles (and their molded products) of the "flash foaming method"
Has various properties, and a high-quality molded product (satisfying practical properties) is obtained from the pre-expanded particles, and the effect of the present invention is obtained. However, if the resin density is in the range of 0.940 g / cm ³ or more, the “molding suitability temperature range” when forming a molded product is extremely narrow, so it is said that an experimental molded product can be created with the mold used for evaluation. In addition, since heating during molding is generally performed by passing steam at a constant temperature (pressure) between the expanded particles filled in the mold, when there is a large difference in thickness between the molded parts, the difference in thickness causes the steam to pass. The pre-expanded particles with a narrow molding suitability temperature range have a steam temperature (pressure) that matches the thicker part of the part.
Then, the thin side of the part becomes overheated, and the steam temperature (pressure) adjusted to the thin side of the part
In that case, the thicker the part, the less heating is achieved, and a good quality molded product cannot be obtained. Therefore, the pre-expanded particles are unsuitable for molding on a production scale in which the fluctuation range of thermal conditions becomes large, and are not possible for molding in a more complicated shape.

On the other hand, the "multi-stage temperature rising foaming method" is more serious, and at least a good molded product can be obtained in all regions of linear low-density polyethylene and linear high-density polyethylene. Shows no results. In particular, in the region where the resin density is 0.940 g / cm ³ or more, it is difficult to obtain the pre-expanded particles having the target ratio by the usual “multi-stage temperature rising foaming method”.

If the pre-expanded particles satisfy the constituent requirements of the invention, they are excellent in various characteristics and of good quality (satisfying practical characteristics).
A molded product will be obtained, and all of the effects of the present invention should be achieved. However, according to the test results of Table 5, even the pre-expanded particles that satisfy the constituent requirements of this description do not always satisfy the effects of the present invention. Furthermore, it is more apparent when linear high-density polyethylene is used as the raw material resin. The description in the above patent publication is an application based on an experimental result that has not been studied at all for at least the foamed particles of the "multi-stage temperature rising foaming method".
From the test results of 1., the description of the actual conditions of the present inventors will be more apparent.

On the other hand, a foam molded article made of polyethylene resin (preliminary) foamed particles is found to be more flexible and elastically cushioned than a foam molded article of polystyrene resin or polypropylene resin. It has been used heavily. In particular, a high-foam molded product having a foaming ratio of 25 cc / g or more is used as a cushioning packaging material for medium to lightweight precision equipment (communication equipment, measuring equipment, office automation equipment, etc.) having a weight of less than 20 kg. The advantage that the material of the cushioning packaging material is polyethylene resin is that the highly elastic and elastic cushioning property of the highly foamed molded product prevents scratches on the surface of the precision instrument and cushions and protects the precision instrument.

[0013]

However, the current market demand in which the price destruction of products is rapidly progressing is that not only the characteristics but also the packaging material (cushioning material) which leads to the product price.
It is creating a trend to strongly reduce the price (total cost) of. This market demand is largely in combination with (1) "reduction of foam transportation cost" and (2) "reduction of resin usage of foam (buffer material)".

First, the transportation cost (transportation cost / storage cost) of the foam according to the market requirement (1) is not based on the weight of the foam but is based on the loadable bulk volume (age). Therefore, the higher the volume of foam, the larger the bulk volume and the uneconomical. In order to reduce the transportation cost of this bulky molded product, it is recommended to make the molding process in-house. That is, a product maker such as a precision instrument that consumes a molded body (buffer packaging material) tries to reduce the transportation cost of the molded body by arranging a small-sized molding process near the packaging process to manufacture the molded body. It is a thing.

Next, the market demand (2) relates to the shape and structure of the cushioning material, which reduces the load receiving area of the cushioning material, the thickness of the cushioning body portion, and the amount of resin used due to high foaming. It is a demand for savings. However, to meet the market demand for reducing the total cost of cushioning packaging materials described above,
At least, it is serious for manufacturers of expanded particles using polyethylene resin as a raw material resin. First, in order to satisfy the above market demand (1), the problem on the production-supply side of the pre-expanded particles is that the molding factories are downsized and dispersed in various places, so that the high-expansion pre-expanded particles are dispersed. It will be transported to molding factories in various places, which will lead to a rise in the transportation cost of expanded particles, and it will be impossible to install expensive expanded particle manufacturing equipment at each factory.

In order to reduce the transportation cost of the pre-expanded particles, it is effective to utilize the advantage of the "multi-stage temperature rising foaming method". The advantage of this "multi-stage temperature-rising foaming method" is that it is a basic stage facility where resin particles are impregnated with a small amount of a foaming agent to form expandable resin particles, which are then transferred to a foaming pot to form expanded particles of low magnification. Apart from this, after that, based on the expanded particles having a low expansion ratio, a foaming agent is pressed into the bubbles of the expanded particles in a pressure vessel to form expandable expanded particles, which are heated and foamed to have a higher expansion ratio. The equipment cost of the process of forming expanded particles is low and the operation technique is easy. Therefore, we have installed this "step of pressurizing and blowing foaming agent" at molding factories dispersed in various places, and we carry out transportation in the state of foamed particles of extremely low foaming, and the amount of foaming necessary for the immediate molding is performed. The operation of "pressing in a foaming agent-heating and foaming" to the particles may be carried out locally, and the transportation cost of the expanded particles (and the transportation cost of the molded product) can be significantly reduced. However, when a non-crosslinked polyethylene-based resin is used as a raw material resin, there is a problem that the essential "multi-stage temperature rising foaming method" cannot be adopted as described above.

Further, in order to satisfy the market demand (2), it is difficult to achieve even the "flash foaming method" for the following reasons, using a polyethylene resin of 0.940 g / cm ³ or more as a raw material resin, and Extremely wide temperature range "
There is a need to complete good quality pre-expanded particles. The reason is that in order to reduce the load receiving area of the cushioning material, the wall thickness of the cushioning material portion, or the high foaming of the market demand (2), the high density side (0.940 g / cm ³ This is because unless the expanded particles obtained by using the polyethylene resin as a raw material resin are used, the basic properties such as rigidity and compressive strength are insufficient and the required cushioning properties cannot be satisfied. Furthermore, there is a demand for reducing the load receiving area of the cushioning material and reducing the wall thickness of the cushioning material part, so that the shape of the cushioning material (mold cavity of the molding die) should be a complicated shape with a large difference in thickness. Therefore, in order to bring out the characteristics of the design value by making the parts with a large difference in thickness equivalent fusion state, it is possible to cope with the heating temperature difference caused by the difference in thickness "extremely wide temperature range suitable for molding". This is because unless the particles are pre-expanded particles, their molding, especially in industrial production, cannot be achieved at all.

However, in the current "multi-stage temperature rising foaming method",
In the high-density side (0.940 g / cm ³ or more) non-crosslinked polyethylene-based resin region, even expanded particles cannot be obtained. Therefore, the expanded particles have not only basic physical properties but also a temperature range suitable for molding. There was nothing but an extremely difficult problem to complete as a wide condition. That is, the object of the present invention is to obtain a resin density of 0.940 g / cm ³
"Multi-stage temperature rising foaming method" that allows easy pre-expanded particles made of polyethylene resin with high density and good physical properties
It is to provide.

[0019]

DISCLOSURE OF THE INVENTION The inventors of the present invention have earnestly studied the above-mentioned "multi-stage temperature rising foaming method", and as a result, the density of 0.940 g / c, which was conventionally considered to be a difficult problem, was realized.
The present invention has found a "multi-stage temperature-increasing foaming method" capable of obtaining "pre-expanded particles (good quality expanded particles) having not only basic physical properties but also a wide molding suitability temperature range" in the polyethylene resin region of m ³ or more. Has been completed. Since the multi-stage temperature-rising foaming method is used, it is possible to take advantage of the fact that the transportation and storage costs of expanded particles can be greatly reduced, and the basic properties of the obtained pre-expanded particles are enhanced, and a wider temperature range suitable for molding is achieved. Therefore, it can be provided as a product that can meet the market demand such as reduction of load receiving area, reduction of foam wall thickness, or high foaming without impairing cushioning characteristics.

The constitution of the production method of the present invention is a method for producing non-crosslinked pre-expanded particles of polyethylene resin, which comprises using polyethylene resin as a raw material resin, impregnating the resin particles with a foaming agent, and foaming the resin. (1) As the raw material resin, the density is 0.920 to 0.930 g /
cm ³ , melting point (mLD) 108 to 118 ° C., high pressure low density polyethylene resin 30 to 50% by weight, and density 0.9.
16 to 0.928 g / cm ³ , melting point (mLL) 118 to
5 to 30% by weight of linear low-density polyethylene resin having a temperature of 123 ° C. and 20 to 45% by weight of linear high-density polyethylene resin having a density of 0.955 to 0.970 g / cm ³ and a melting point (mHD2) of 128 to 135 ° C. And a density of 0.940-0.
954 g / cm ³ , melting point (mHD1) is [(mHD2 +
mLL) ÷ 2] 10 to 35% by weight of the linear high-density polyethylene resin in the range of ± 2 ° C, and the density of the mixed resin consisting of the four components is 0.940 to 0.952 g /
using a mixed resin that is cm ³ .

(2) When the resin particles are impregnated with a foaming agent, the resin particles are impregnated with the foaming agent.
This is heated to form low-foamed particles having an expansion ratio of 1.5 to 3.5 cc / g, and then the foaming agent is impregnated into the cells of the low-foamed particles, and this is heated to obtain a higher expansion ratio. A method for producing non-crosslinked pre-expanded particles of polyethylene resin, which is characterized in that a multistage temperature rising foaming method for forming expanded particles is used. Preferably, the step of forming expanded particles having a higher expansion ratio is repeated 2 to 4 times to obtain an expansion ratio of 6 to 60 cc / g.
It is also a method for producing non-crosslinked pre-expanded particles of a polyethylene-based resin, characterized in that

The contents of the present invention will be described below. The present invention is different from the prior art in the following: 1) In forming pre-expanded particles having a resin density of 0.940 to 0.952 g / cm ³ , a raw resin to be expanded particles is mixed with the above-mentioned specific four components. Using a resin, 2) once the resin particles have an expansion ratio of 1.5-in the process until the resin particles have an expansion ratio of 6-60 cc / g.
After the foaming step of forming expanded particles of 3.5 cc / g, a foaming agent is press-fit into the bubbles of the obtained expanded particles, and this is heated and expanded to form expanded particles having a higher expansion ratio. Adopting the "temperature rise foaming method", 1) above
It is in the combination of 2).

First, the technical significance of the above requirement 1) will be described. First, the resin density of the pre-expanded particles is 0.940.
The significance of being 0.952 g / cm ³ will be described. The meaning that the density is 0.940 g / cm ³ or more defines the basic characteristics of the intended polyethylene resin pre-expanded particles (and molded body). Also, the density is 0.940 g / c
Conventionally, the polyethylene-based resin in the region of m ³ or more is also a resin in the region where it is difficult to apply to the “multi-stage temperature rising foaming method” in a non-crosslinked state. The meaning of 0.952 g / cm ³ or less is the upper limit density of the mixed resin which can be obtained with the composition component of the resin shown in the present invention. (Note that the substantial effect of increasing the density of the polyethylene resin described here will be described later with reference to FIG. 7.)

Next, the technical significance of using the mixed resin of the specific four components of the present invention as the polyethylene resin will be described. 1 to 6 are respective melting endothermic curves measured by a differential scanning calorimeter (DSC) of each raw material resin after being heated to a temperature for foaming and then cooled. This melting endotherm curve is
Perkin-Elme (Perkin-Elme)
r) A sample of about 10 mg was used for 1
3 is a melting curve when the temperature is raised from 30 ° C. to 200 ° C. at a rate of 0 ° C./min. The baseline of the melting endotherm is from 80 ° C to the end of melting. Then, based on this baseline, the temperature corresponding to 50% of the heat of fusion of the entire resin (area surrounded by the melting endothermic curve and the baseline) is T5O, and the temperature corresponding to 70% of heat of fusion is T7O. There is.

FIG. 1 is a mixed resin consisting of four specific components of the present invention (Experiment No. 1) and having a density of 0.944 g / cm ³ , FIG.
Is a comparative product (Experiment No.) and has a density of 0.924 g / cm ^3.
Linear low density polyethylene resin, Fig. 3 is a comparative product (experimental No. E) and has a density of 0.935 g / cm ³ linear low density polyethylene resin, and Fig. 4 is a comparative product (experimental No. N). 0.945 g / cm ³ linear high-density polyethylene resin, FIG. 5 shows a comparative product (Experiment No. 32) of high-pressure low-density polyethylene resin, linear low-density polyethylene resin, and linear high-density polyethylene resin. Consist of 3 components and density 0.9
35 g / cm ³ mixed resin, FIG. 6 shows a comparative product (Experiment No.
31) in high pressure method low density polyethylene resin, linear low density polyethylene resin, linear high density polyethylene resin 3
The case of mixed resin composed of the components and having a density of 0.944 g / cm ³ is shown respectively.

Here, the sample object in each figure is the "resin after being heated to the foaming temperature", and the "temperature range between T50 and T70 (corresponding to the heat of fusion of 50 to 70% of the total)" is used as an index. The reason is that the resin (crystal) state at the time of foaming to obtain the expanded particles has already changed from the original state of the resin (crystal) due to the heating for foaming, and the heating at the time of foaming to obtain the expanded particles is the resin. This is because it is empirically known that 50 to 70% of the above is performed in a molten state. That is, if the resin is melted at less than 50%, homogeneous foaming cannot occur, and if melted at more than 70%, fusion between particles is extremely advanced, or the resin is violently flowed and the shape of particles having a regular cell structure cannot be maintained. It will be.

According to the knowledge of the present inventors, the most important condition in the "multi-stage temperature-rising foaming method" is to obtain good quality foamed particles having a homogeneous cell structure in the first foaming. The “temperature range between T50 and T70 = (foaming suitability temperature range)” of the resin sufficient to obtain expanded particles is at least 6
It has been observed and confirmed that ℃ is required.

Based on the above findings, each "T5" shown in FIGS.
"Temperature range between 0 and T70", the resin satisfying the condition of "at least 6 ° C" is the mixed resin of the special four components of the present invention shown in Fig. 1 and having a density of 0.944 g / cm ³ (temperature range). Approximately 7 ° C), consisting of the three components in Fig. 5, density 0.933g
/ Cm mixed resin (a temperature ranging from about 7 ° C.) of ³ or two alone, in Figure 2 the density 0.924 g / cm ³ of linear low density polyethylene resin, density 0.935 g / cm ³ in FIG. 3 Linear low density polyethylene resin, density 0.945g in Figure 4
/ Cm ³ linear high density polyethylene resin, when the resin of 3 Density consists ingredient 0.944 g / cm ³ mixed resin of Figure 6, the temperature range is respectively about 5 ° C., to about 3 ° C., about 2
It can be seen that the temperature is about 4 ° C. and does not satisfy the condition of “at least 6 ° C.”. The results for the “temperature range between T50 and T70” shown in FIGS. 1 to 6 are in agreement with the test results for the “multi-stage temperature rising foaming method” shown in Table 5, and particularly, for the conventional product. This supports the fact that polyethylene resins having a density of 0.940 g / cm ³ or more are difficult to be suitable for the “multi-stage temperature rising foaming method”.

Then, comparing the one of FIG. 1 (special four-component mixed resin of the present invention) which is suitable for the "multi-stage temperature rising foaming method" and the one of FIG. 5 (three-component mixed resin), the mixed resin The density of the former is 0.944 g / cm ³ , whereas the latter is 0.933 g / cm ³ . A polyethylene resin with a density of 0.940 g / cm ³ or more, which is suitable for the "multi-stage temperature rising foaming method",
It can be seen that only the specific four-component mixed resin of the present invention in FIG. 1 is used.

Of the four specific components, the notable one is the fourth one.
Density 0.940-0.954g used as an ingredient
/ Cm ³ , melting point (mHD1) is [(mHD2 + mLL)
÷ 2] The linear high-density polyethylene resin in the range of ± 2 ° C is used in an amount of 10 to 35% by weight.

The first role of this fourth component resin is the other three
By increasing the compatibility between the linear low-density polyethylene resin and the linear high-density polyethylene resin among the components, the whole mixed resin is integrally compatible, and the molecular segment of each resin is The entanglement of the mixed resin was increased, and the flow viscosity as if a mixed crystal of the mixed resin was formed was exhibited. The second role is to fill the melting point difference between the linear low-density polyethylene resin and the linear high-density polyethylene resin among the other three components, so that even if it is a mixed resin, one melting point That is, the resin has a melting endothermic curve similar to that of the resin. These two roles improve the moldability of the obtained pre-expanded particles (expand the temperature range suitable for molding).
Then, for example, in a molded article having a complicated shape in which portions having greatly different thicknesses are mixed, fusion of the foamed particles forming each portion of the molded article having different thicknesses becomes a uniformly fused molded article everywhere. Produces the effect of saying. The improvement of the fusion property of each part of the molded product is an important factor for making the basic properties in a state where the basic properties can be exhibited as designed, and the high density (0.
The resin has basic properties of 940 to 0.952 g / cm ³ ), and as a result, it becomes possible to reduce the load receiving area of the cushioning material and the thickness of the foam.

In FIG. 7, the symbol ⊚ in the figure is for a mixed resin consisting of the specific four components of the present invention and having a density of 0.944 g / cm ³ , and the symbol □ is a linear resin having a density of 0.924 g / cm ^3. A low density polyethylene resin is also shown. The abscissa represents the density (kg / m ³ ) of the molded product [the expansion ratio (cc / g) is shown together], and the ordinate represents the compression strength (kg / cm ² ) of the molded product. The relationship of strength is represented on a logarithmic scale. The compressive strength adopted here is a basic property that governs the cushioning performance of the molded body.

The difference in the magnitude of compressive strength shown in FIG. 7 is the effect of increasing the density of the polyethylene resin from 0.924 g / cm ³ to 0.944 g / cm ³ . Specifically, the conventional density 0.924 g / cm ³ of linear low density polyethylene resin of the same damping characteristics as the foamed molded as a raw material resin, the 4-component mixed resin of density 0.944 g / cm ³ material When attempting to exert the effect on the foamed molded article, the reduction of the load receiving area of the cushioning material, the thickness of the foamed body, or the high foaming of the molded body is caused by the difference in the compression strength. It means that you can achieve it. As described above, the upper and lower limits of the density, melting point, and composition ratio of the resin composed of the specific four components described above are defined by the high density (0.
940 to 0.952 g / cm ³ ), and is an indispensable requirement for exerting the above-mentioned effects on it.

Next, the technical significance of the above requirement 2) will be described. First, the expansion ratio of the pre-expanded particles is 6 to 60 cc / g.
The requirement is to provide the cushioning properties of the shaped body with a wide range of choices. That is, the foamed molded article is obtained by subjecting the expanded beads to in-mold heat molding. Therefore, the expansion ratio of the obtained foamed molded product tends to increase due to expansion during molding, but this increase is not so large, so that the target expansion ratio of the molded product is mainly determined by the expansion ratio of the pre-expanded particles to be used. On the other hand, the expansion ratio of the molded body to be used as the cushioning material should be considered in consideration of the compressive strength that can withstand the weight of the packaged object, the elastic cushioning capacity sufficient to absorb the impact at the time of impact and the thickness of the cushioning material portion. Establish. This is to provide the cushioning property exhibited by the molded body in a wide range of freedom of selection. Further, the expansion ratio of the pre-expanded particles is preferably 16 to 60 cc / g on the high expansion ratio side in consideration of the buffering characteristics of the main application.

Further, once the resin particles are expanded with an expansion ratio of 1.5 to
The need to make expanded particles of 3.5 cc / g means that in the subsequent expansion (expansion) step, pre-expanded particles of high quality and high expansion ratio are economically produced, and transportation and storage are most economically performed. It is in harmony with the selection of a low expansion ratio. That is, 1.5
With a low expansion ratio of less than cc / g, the absolute number of cells and the volume of the cells are insufficient, and the pressure (expansion ability) of the foaming agent required to expand the expanded particles in the subsequent step is insufficient, resulting in high quality. The disadvantage is that pre-expanded particles cannot be obtained, and the pressure-injection of this foaming agent precludes the use of economical equipment. On the other hand, when the expansion ratio is higher than 3.5 cc / g, the foam structure is apt to be disturbed in the subsequent expansion process, and it becomes difficult to obtain high quality pre-expanded particles, and the fovea height becomes high and the economy during transportation and storage is high. It will worsen the sex. From the viewpoint described above, foaming with the foaming agent in the first stage requires that the expansion ratio be 1.5 to 3.5 cc / g expanded particles, and the expansion ratio is 1.8 to 3.0 cc / g. It is desirable to use the expanded particles of

Next, "the multi-stage temperature-rising foaming method in which at least one step of impregnating the cells of the obtained foamed particles with a foaming agent and thermally expanding the foaming agent to obtain expanded particles having a higher expansion ratio" is carried out. The meaning to be adopted is that the expansion ratio is 1.5 to 3.5 cc / g in order to satisfy the above economical efficiency during transportation and storage.
This is because it is possible to easily form the final expanded foamed particles having a high expansion ratio with an economical device at the molding site. The equipment cost of a device (container, piping, etc.) for press-fitting the foaming agent into the bubbles of the primary expanded particles varies depending on the pressure handled by the device. For example, the current Japanese law is 10k.
A device that handles a pressure higher than g / cm ² is subject to the High Pressure Gas Regulation Law, and it is necessary to install a device with a high degree of safety against pressure, and accompanying equipment is also required. In addition, it is obliged to regularly perform the pressure resistance inspection, and the inspection standard is strictly evaluated. Therefore, the equipment cost is naturally high, and further, a trained and licensed worker is required to handle the device. On the other hand, devices that handle pressures less than the above are not subject to strict regulations, so the device can be made very inexpensive,
Further, it can be operated by a normal worker. "Multi-stage temperature rise foaming method"
In the above, apart from the first-stage primary foaming process, the subsequent press-in of the foaming agent and the foaming process of the foamed particles can be carried out by the above-mentioned extremely inexpensive apparatus if carried out stepwise.
That is, the pressure for handling is lower than 10 kg / cm ² by performing the expansion operation in multiple stages so as to reduce the ratio of the expansion ratio of the original expanded particles to the expansion ratio of the final expanded particles. This is because it can be

Further, this step is particularly expressed as 2 to 4 times when the expansion ratio of the original expanded particles is 3.5 cc.
Even if it is carried out in one step to obtain a final expanded particle having an expansion ratio of 6 cc / g, the handling pressure is 3 Kg.
/ Cm ² of about but of not only one, the tentatively ones expansion ratio of the original foamed particles of 1.5 cc / g, with the expansion ratio 6
When making the final expanded particles of 0 cc / g, if the pressure is handled in 4 stages (for example, evenly divided magnification), the pressure to be handled will be about 9 Kg / cm ² at the maximum, and the pressure to be handled will be 1
It can be of lower pressure, less than 0 kg / cm ² . Specifically, for example, the target expansion ratio in the initial expansion is kept at 2.5 cc / g, and the target expansion ratio in the first expansion is set to 9 cc / g, and the target expansion ratio in the second expansion is set. Is 16 cc / g, the target expansion ratio in the third expansion is 33 cc / g, and the target expansion ratio in the fourth expansion is 60 cc / g. Ideally, the handling pressure is 9 kg / cm ² at maximum. Also, in this case, if the expansion ratio of the expanded particles used for transportation is 2.5 cc / g, the bulk volume will be about 1/6 that of the case where the expansion ratio is 16 cc / g and the expansion ratio will be Is about 1/12 of that when transported at 30 cc / g, which is efficient. On the other hand, increasing the number of this expansion stage increases the labor of the operation and becomes uneconomical. In the case of the present invention, 1.
This is because it is possible to efficiently obtain high-quality pre-expanded particles by performing the expansion step in the range of up to 4 steps while keeping the expansion ratio to 5 to 3 times.

Next, the high-pressure low density polyethylene (LDPE) used for the raw material resin used in the present invention has a density of 0.920 to 0.930 g / cm ³ and a melting point of 98 to 11.
8 ° C, MI (melt index: 190 ° C, 2.16
kg) 0.05 to 30 g / 10 minutes. Linear low-density polyethylene (LLDPE) is a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms, and the α-olefin is propylene, butene-1, pentene-.
1, hexene-1, heptene-1, octene-1, 4-
Methyl pentene-1,1-decene, 1-tetradecene,
1-octadecene and the like, and one or two of these
It may be a mixed component of two or more kinds. The composition ratio of α-olefin is 2 to 10 mol%, and the density is 0.916 to 0.
928 g / cm ³ , melting point of 118 to 123 ° C., MI of 0.
1 to 30 g / 10 minutes. Linear high-density polyethylene (HDPE) is ethylene and α having 3 to 10 carbon atoms.
It is a copolymer with olefins, the composition ratio of α-olefin is less than 2 mol%, and due to its density, HD with low density
There are two types, 1 and HD2 having high density. HD1
Has a density of 0.940 to 0.954 g / cm ³ and a melting point of 123
˜129 ° C., MI of 0.05 to 30 g / 10 minutes. HD2 has a density of 0.955 g / cm ³ or more and a melting point of 1
28-135 degreeC and MI are 0.05-30 g / 10min.

The non-cross-linked polyethylene resin particles of the present invention are preferably in a non-cross-linked state, but may be cross-linked to some extent within the range where re-pelleting is possible. The rate is 10% or less. In the present invention, for example, various fillers, antioxidants, light stabilizers, antistatic agents, flame retardants, lubricants, nucleating agents, pigments, dyes, etc. may be blended with the raw material resin.

In the present invention, the foaming agent used to obtain the primary expanded particles from the resin particles is preferably one having a boiling point not higher than the softening temperature of the resin and having high solubility in the resin, such as carbon dioxide and propane. , Butane, pentane, 1-1
-1-2 tetrafluoroethane (F-134a), 1-
1 difluoroethane (F-152a), methylene chloride,
Examples thereof include ethylene chloride. Among them, carbon dioxide that clears the CFC regulations and is nonflammable is a desirable foaming agent. The content of the foaming agent varies depending on the type of the foaming agent and the degree of the desired expansion ratio, but is usually 0.1 to 0.1%.
It is 1.0 mol / kg. The temperature and the pressure when the particles contain the foaming agent are arbitrary, and the method of impregnating the foaming agent may be either gas phase or liquid phase, and is not particularly limited. Further, as the foaming agent for foaming the primary expanded particles in multiple stages, those having a boiling point not higher than the softening temperature of the resin and having a small gas permeability coefficient are preferable, and an inorganic gas such as nitrogen or air is used.

The resin density (g / cc) referred to in the present invention is
It is a value measured according to ASTM D-1505. The melting point (° C) referred to in the present invention is about 30 mg of a sample of about 10 mg at a rate of 10 ° C / min, using a DSC-7 type manufactured by Perkin-Elmer as a measuring device.
After raising the temperature from ℃ to 200 ℃, hold the temperature for 1 minute, cool and crystallize to 30 ℃ at a rate of 10 ℃ / min, hold the temperature for 1 minute, and again at a speed of 10 ℃ / min It is obtained from the peak value of the melting curve when the temperature is raised. Moreover, the evaluation method of the characteristic value and the evaluation scale used in the present invention were performed as follows.

[Expansion Ratio (cc / g) of Expanded Particles] Weight (Wg) This is a value obtained by measuring the volume (Vcc) of known expanded particles by the water immersion method and dividing the volume by the weight. [Closed cell ratio (%)] It was measured by the air pycnometer method (manufactured by BECMAN, model 930) described in ASTM D-2856. Average of n = 10.

[Average Cell Diameter (mm)] The number of bubbles per arbitrary length L (1 mm or more) on each of the three-dimensional axes obtained by cutting the expanded particles at three orthogonal planes. It is a value obtained by reading the number and using the following equation. Average cell diameter (mm) = L (mm) / number of cells [Oil resistance] Pre-expanded particles were added to edible oil, and the state of deformation after 3 hours was evaluated.

Evaluation scale Classification Symbol Shrinkage of less than 0.5% of original volume ◎ Shrinkage of less than 2.0% 0.5% or more ○ Shrinkage of less than 5.0% 2.0% or more △ 5.0% or more Contraction of ×

[Weather Resistance] The treated product was treated with a weather meter for 200 hours, and the treated product was judged separately for the following two items. 1. Coloring of particles by visual inspection, deformation evaluation scale Classification symbol No coloring or deformation at all ◎ Slight coloring or deformation is observed ○ Coloring or deformation is observed △ Coloring or deformation is significantly observed ×

2. Change in compression elastic value Evaluation scale Classification symbol Reduction rate of compression elastic value is less than 5% ◎ Reduction rate of compression elastic value is 5% or more and less than 10% ○ Reduction rate of compression elastic value is 10% or more and 20% Less than △ Reduction rate of compression elastic value is 20% or more × * Reduction rate of compression elastic value% = (compression elastic recovery rate before test-compression elastic recovery rate after test) ÷ compression elastic recovery before test Rate x 100

[Heat resistance] 100 ° C. in a gear oven
After 1000 hours, the following two items were evaluated separately. 1. Coloring of particles by visual inspection, deformation evaluation scale Classification symbol No coloring or deformation at all ◎ Slight coloring or deformation is observed ○ Coloring or deformation is observed △ Coloring or deformation is significantly observed ×

2. Change in compression elastic value Evaluation scale Classification symbol Reduction rate of compression elastic value is less than 5% ◎ Reduction rate of compression elastic value is 5% or more and less than 10% ○ Reduction rate of compression elastic value is 10% or more and 20% Less than △ Reduction rate of compression elastic value is 20% or more × * Reduction rate of compression elastic value% = (compression elastic recovery rate before test-compression elastic recovery rate after test) ÷ compression elastic recovery before test Rate x 100

[Flexibility] Judgment was made based on the angle at which the molded product having a thickness of 30 mm molded in the mold was broken when it was bent. Evaluation scale Classification symbol Do not break up to 180 ° ◎ Break at 90 ° to 180 ° ○ Break at 45 ° to 90 ° △ Break at 45 ° or less ×

[Tear strength] It was measured according to JIS K-6767. Classification symbol Exceeds 7 kg / 10 mm width ◎ Exceeds 2 kg / 10 mm width 7 kg / 10 mm width or less ○ Exceeds 1 kg / 10 mm width 2 kg / 10 mm width or less △ 1 kg / 10 mm width or less ×

[Flexural fatigue resistance] Measured according to JISP-8115. Classification symbol No break 500 times or more ◎ Breaks 300 to less than 500 times ○ Breaks 100 to less than 300 times △ Breaks less than 100 times ×

[Compression resistance] Ten meters using Tensilon
It was compressed to a maximum stress of 4 kg / cm ² at a speed of m / min, the stress was removed, and the elastic recovery from strain after 24 hours was measured. Classification symbol 95% or more recovered ◎ 90 to less than 95% recovered ○ 85 to less than 90% recovered △ less than 85% recovered ×

[In-mold formability] In the obtained molded product having a shape corresponding to the space inside the mold where the beads are filled in FIG. 8, the obtained part A (thickness about 50 mm), B in FIG. The fusion degree and dimensional shrinkage with respect to the mold at each measurement site indicated by the part (thickness: about 13 mm) and the C part (thickness: about 15 mm) are evaluated according to the following criteria, and whether good in-mold hot molding is possible It was evaluated as follows. Evaluation scale Classification symbol Fusion degree, mold shrinkage to mold ◯ Both molding foams are obtained ○ Fusion degree, mold dimensional shrinkage ratio △ Either molding foam is obtained Melt Adhesion and mold dimensional shrinkage x both are △ or ×

* Fusion degree A square test piece of 30 × 30 mm is cut out from the molded product, a cut with a depth of 2 mm is made in the center thereof, and the molded product is cleaved by bending along the cut to exist in the cut cross section. The percentage of the number of particles ruptured and broken in the bubble portion with respect to the total number of particles was calculated. Classification Symbol Remarks When the material breakage rate is 80% or more ○ Excellent When the material breakage rate is less than 80% or 60% or more △ Good When the material breakage rate is less than 60% × Poor

* Shrinkage of mold with respect to mold The shrinkage of the molded foam with respect to the mold was evaluated as follows. Category Symbol Remarks 4% or less ○ Excellent 4% to 6% or less △ Good 6% or more × Poor

[Molding Appropriate Temperature Range] When a molded foam product having both the above-mentioned degree of fusion and dimensional shrinkage with respect to the mold is ◯, the upper limit of the steam pressure for molding heating for obtaining a good product is set. The lower limit difference was defined as the temperature range suitable for molding, and the following evaluation was made. According to rating scales classification Remark 0.14 kg / cm ² or more when superior 0.14 kg / cm ² less than 0.08 kg / cm ² or more when good 0.08 kg / cm ² less than in the case defective Compression Strength] JISK-6767 Measured. Two
It is a compressive stress value when a 5% compressive strain is generated.

[0057]

[Examples] The polyethylene resins used in Examples, Comparative Examples and additional experiments are 11 kinds shown in Table 3. The basic conditions of the method for producing pre-expanded particles by the multi-stage temperature rising foaming method and the method for producing a molded body used in Examples, Comparative Examples and additional experiments are as follows.

(1) Resin particle manufacturing process The resins shown in Table 3 were melt-kneaded at the composition ratios in each example by using a twin-screw extruder, extruded in a strand form from a die attached to the tip of the extruder, and water. It was cooled and cut into particles having a diameter of 0.7 mm and a length of 1.3 mm to manufacture. (2) Expanded particle manufacturing process Here, the target magnification of 2.5 cc / g in the expanding process is
The target magnification is 9.0 cc / g in the first expansion, the target magnification is 16 cc / g in the second expansion, the target magnification is 33 cc / g in the third expansion, and the target magnification is 60 c in the fourth expansion.
It was carried out by using the multistage temperature rising foaming method at which an ideal expanded particle of c / g was obtained.

<< Low Foaming Step >> The resin particles obtained by the above method are placed in a pressure vessel and carbon dioxide (gas) is used as a foaming agent.
Was injected and carbon dioxide was impregnated into the resin particles for 2 to 4 hours under the conditions of a pressure of 30 kg / cm ² G and a temperature of 8 ° C.
The impregnation amount of carbon dioxide was adjusted by the impregnation time so as to be 1.6 parts by weight. Next, the expandable resin particles were housed in a foaming device (deaeration temperature raising system), the temperature inside the tank was raised from 80 ° C. to the foaming temperature over 20 seconds, and steam was kept for 10 seconds while maintaining the temperature. Heat-expanded to obtain primary pre-expanded particles. For the foaming temperature, the optimum condition was obtained in advance in the following preliminary experiment for each resin and adopted. That is, in the water vapor pressure, 1.80 kg from 0.50kg / cm ² G / cm ²
The primary pre-expanded particles obtained by adjusting each step in the range of G in increments of 0.05 kg / cm ² were aged at room temperature for 1 day, and then the expansion ratio and closed cells were evaluated according to the above-mentioned evaluation methods according to the expansion temperature. The rate and the average bubble diameter are measured. From each of these measurement results, the target expansion ratio is close to 2.5 cc / g,
The closed cell ratio is high, and the average bubble diameter is 0.15mm.
The optimum foaming temperature of the resin is one that is close to and has the same value.

<< First Expansion >> Primary pre-expanded particles having an expansion ratio of 2.5 cc / g obtained in the low expansion step were housed in a pressurizing / warming device and kept at a temperature of 80 ° C. for 1 hour. The pressure of the air was increased and the pressure was maintained at 8.5 kg / cm ² G for 5 to 8 hours to increase the internal pressure of gas (air) in the expanded particles. The amount of air in the expanded particles obtained by this treatment is 6 kg / cm ² G by pressure.
The holding time was adjusted so that Next, the expanded resin particles to which the internal pressure was applied were housed in a foaming device (a deaeration temperature raising system), and the temperature inside the tank was raised from 80 ° C. to the expansion temperature over 20 seconds while further maintaining the temperature. Steam heating for 10 seconds gave secondary pre-expanded particles. Regarding the expansion temperature, the optimum conditions were determined in advance in the following preliminary experiment for each primary expanded particle and adopted. That is, at steam pressure, 0.50 kg /
0.05 in the range of cm ² G to 1.80 kg / cm ² G
adjusted in kg / cm ² increments, after aging for 1 day the secondary pre-expanded particles obtained in each of the expansion temperature at room temperature, expansion ratio by the evaluation methods described above according to different expansion temperature, closed cell ratio, average cell diameter To measure. From each of these measurement results, the optimum expansion temperature of the resin is determined to be close to the target expansion ratio of 9.0 cc / g, to have a high closed cell rate, and to have an average cell diameter close to the target value of 0.26 mm and with a uniform value. did.

<< Second Expansion >> The secondary pre-expanded particles having the expansion ratio of 9.0 cc / g obtained by the first expansion are pressed.
The mixture was housed in a warming device, the air pressure was increased at a temperature of 80 ° C. over 3 hours, and the pressure (5.0 kg / cm ² G) was maintained for 3 to 5 hours to increase the gas (air) internal pressure of the expanded particles. The amount of air in the expanded particles obtained by this treatment is 2.5 kg / cm by pressure.
^The holding time was adjusted so as to be ² G. Next, a foaming device (deaeration temperature raising method) is used to expand the expanded resin particles to which the internal pressure is applied.
And the temperature in the tank was raised from 80 ° C. to the expansion temperature over 20 seconds, and the temperature was maintained, and steam heating was performed for 10 seconds to obtain tertiary pre-expanded particles. As for the expansion temperature, the optimum condition was obtained in advance in the following preliminary experiment for each secondary expanded particle and adopted. That is, at steam pressure, 0.50k
g / cm ² G to 1.80 kg / cm ² G in the range of 0.
After adjusting the pressure in increments of 05 kg / cm ^{2 and} aging the tertiary pre-expanded particles obtained at each expansion temperature for 1 day at room temperature, the expansion ratio, closed cell ratio, and average cell diameter were evaluated according to the above-mentioned evaluation methods according to the expansion temperature. taking measurement. From these measurement results, the optimum expansion temperature of the resin was determined to be close to the target expansion ratio of 16 cc / g, to have a high closed cell rate, and to have an average cell diameter close to the target value of 0.32 mm and a uniform value. The fact that the target magnification was not reached was noted as "no foaming".

<< Third expansion >> The third pre-expanded particles having an expansion ratio of 16 cc / g obtained in the second expansion are housed in a pressurizing / warming device and air is kept at a temperature of 80 ° C. for 5 hours. Was increased and the pressure was maintained at 5.0 kg / cm ² G for 1 to 3 hours to increase the gas (air) internal pressure of the expanded particles. The amount of air in the expanded particles obtained by this treatment is 3.0 kg / cm ^{2 in} terms of pressure.
The holding time was adjusted so that G was obtained. Next, the expanded resin particles to which the internal pressure was applied were housed in a foaming device (a deaeration temperature raising system), and the temperature inside the tank was raised from 80 ° C. to the expansion temperature over 20 seconds while further maintaining the temperature. Steam heating was performed for 10 seconds to obtain quaternary pre-expanded particles. As for the expansion temperature, the optimum condition was obtained in advance in the following preliminary experiment for each tertiary expanded particle, and it was adopted. That is, at steam pressure, 0.50 kg
/ Cm ² G to 1.80 kg / cm ² G in the range of 0.0
Adjusted with 5 kg / cm ² increments, after aging for 1 day quaternary pre-expanded particles obtained in each of the expansion temperature at room temperature, expansion ratio by the evaluation methods described above according to different expansion temperature, closed cell ratio, average cell diameter To measure. From these measurement results, the optimum expansion temperature of the resin was determined to be close to the target expansion ratio of 33 cc / g, to have a high closed cell rate, and to have an average cell diameter close to the target value of 0.40 mm and a uniform value. The fact that the target magnification was not reached was noted as "no foaming".

<Fourth expansion> The fourth pre-expanded particles having an expansion ratio of 33 cc / g obtained by the third expansion were housed in a pressurizing / warming device and the temperature was 80 ° C. for 5 hours. The pressure of air was increased and the pressure (7.0 kg / cm ² G) was maintained for 2 to 4 hours to increase the gas (air) internal pressure of the expanded particles. The amount of air in the expanded particles obtained by this treatment is 2.5 kg / cm ² under pressure.
The holding time was adjusted so that G was obtained. Next, the expanded resin particles to which the internal pressure was applied were housed in a foaming device (a deaeration temperature raising system), and the temperature inside the tank was raised from 80 ° C. to the expansion temperature over 20 seconds while further maintaining the temperature. Steam heating was performed for 10 seconds to obtain fifth pre-expanded particles. As for the expansion temperature, the optimum condition was obtained in advance in the following preliminary experiment for each quaternary expanded particle, and it was adopted. That is, at steam pressure, 0.50 kg
/ Cm ² G to 1.80 kg / cm ² G in the range of 0.0
After adjusting at 5 kg / cm ² increments and aging the 5th pre-expanded particles obtained at each expansion temperature at room temperature for 1 day, the expansion ratio, closed cell ratio and average cell diameter were determined according to the evaluation methods according to the expansion temperature. To measure. From the respective measurement results, the optimum expansion temperature of the resin was determined to be close to the target expansion ratio of 60 cc / g, to have a high closed cell rate, and to have the average cell diameter close to the target value of 0.50 mm and the values were uniform. The fact that the target magnification was not reached was noted as "no foaming".

(3) Process for producing molded body The pre-expanded particles obtained by the above method etc. are allowed to stand for 48 hours at room temperature and normal pressure, and then filled in a pressure vessel to 2.5 kg / cm ² G
It was aged under pressure for 48 hours. Then, in a mold of a general type in which the pre-expanded particles are attached to a molding machine {when the two male and female molds are fitted, the internal space thereof shows the dimensions of each part in FIG. 300, 300, 50m
m, part A (thickness 50 mm), part B (thickness 13 mm),
As shown in FIG. 9, a generally used steam inflow member is arranged at a pitch of 20 mm on the mold cavity for forming the inner dimension of the thick and thin part of the C portion (15 mm in thickness), and the entire inner surface of the male and female molds. Was filled in, molded by heating, cooled, and taken out from the molding die to obtain a molded foam.

[0065] forming temperature "Evaluation method of moldability temperature range" was adjusted molded in at 0.02 kg / cm ² G increments range 1.00~2.00kg / cm ² G steam pressure, each forming The molded product obtained at the temperature was cured and dried at 70 ° C. for 20 hours, left at room temperature for 1 day, and then the fusion degree and the dimensional shrinkage ratio with respect to the mold were measured according to the above-mentioned evaluation methods according to the molding temperature. The temperature range suitable for molding at which a molded product was obtained was investigated. When there was no molding temperature at which a good molded product was obtained, it was described as "none". At the same time, from this result, the optimum molding temperature at which the best molded product was obtained was selected.
Then, molding was performed again at this selected molding temperature to obtain a molded product, and the in-mold moldability and the characteristics of the molded product were evaluated by the evaluation methods described above.

(Example-1, Comparative Example-1) The experiment here is for showing the range of the resin component in the present invention. In the following experiment, based on the above-described method for producing pre-expanded particles, resin particles in Table 4 were prepared with a mixing ratio composition corresponding to each experiment number, and the foaming condition section in Table 2 was used. The pre-expanded particles having an expansion ratio of 16 cc / g were manufactured by performing the low expansion, the first expansion, and the second expansion steps at the expansion and expansion temperatures selected in advance in the respective experiment number columns. For each of the obtained expanded particles, the expansion ratio by the evaluation method, the closed cell ratio, the average cell diameter, and based on the method for producing a molded body described above,
The temperature range suitable for molding was evaluated, and the results are shown in Table 4.

According to the results of Table 4, those obtained by manufacturing from the resin component region of the present invention (Experiment Nos. 1 to 3 are in the enclosure of the component region, and Experiment Nos. 4 to 15 are the limit points of the component region. Indicates that the target pre-expanded particles having an expansion ratio of 16 cc / g can be obtained and a good product can be obtained in a wide moldability temperature range, and the in-mold moldability during production is excellent. On the other hand, what was obtained by manufacturing from a region other than the component of the present invention used as a comparative example (Experiment Nos. 16 to 23) could obtain a target pre-expanded particle having an expansion ratio of 16 cc / g. , 16 cc / g of the target pre-expanded particles can be obtained, it can be seen that the molding temperature range for obtaining a good product is narrow. This result reveals that the range of the resin component of the present invention is necessary for achieving the purpose of the present invention.

(Example-2, Comparative Example-2) The experiment here is to show the importance of using a specific four-component mixed resin as the raw material resin for the pre-expanded particles in the present invention. It is a thing. The following experiment was carried out based on the above-mentioned method for producing pre-expanded particles, in which the resin particle section of Table 5 was prepared with a mixing ratio composition corresponding to each experiment number, and the foaming condition section of Table 5 was prepared. The expansion ratio of 16 cc / is obtained by performing the low expansion, first expansion, and second expansion steps at the preselected foaming and expansion temperatures described in each experiment number column of
For the pre-expanded particles of 16 cc / g, the pre-expanded particles of 16 cc / g were further expanded a third time to produce pre-expanded particles having an expansion ratio of 33 cc / g.

Experiment No. Nos. 24 to 26 are the same as Experiment No. 1 of Example-1. Foaming ratio of 16 cc / g obtained in 1-3
A third expansion was performed using the third expanded beads of to produce pre-expanded particles having an expansion ratio of 33 cc / g. With respect to each of the obtained expanded particles, the expansion ratio, closed cell ratio, average cell diameter, oil resistance, weather resistance-1, 2 and heat resistance-1, 2 were evaluated by the above evaluation method, and the results are shown in Table 5. 6 shows. Further, for each of the obtained expanded particles, based on the method for producing a molded article described above, the molding suitability temperature range is set to the molding condition described in the molding condition section of Table 6 where the best molded product is obtained. The molded product was remolded at a temperature, and the obtained molded product was used to evaluate the expansion ratio, flexibility, tear strength, flex fatigue resistance, compression elasticity, and compression strength by the above evaluation method. The results are shown in Table 6.
Shown in

According to the results shown in Tables 5 and 6, those obtained from the specific four-component mixed resin of the present invention having a resin density of 0.940 g / cm 3 or more (Experiment Nos. 1 to 3 and Experiment No. 3).
24-26) is a foaming ratio of 16 cc / g, 33 cc / g
It can be seen that the target pre-expanded particles can be obtained and a good product can be obtained, and the moldability temperature range is wide, and the in-mold moldability during production is excellent. On the other hand, a comparative product lacking one or more of the four components of the present invention used as a comparative example, that is, a mixed resin of LL / HD1 / HD2 (Experiment No. 2).
7), HD1 / HD2 mixed resin (Experiment No. 28),
LL / HD1 mixed resin (Experiment No. 29), LL / H
D2 mixed resin (Experiment No. 30), LD / LL / HD
The product obtained from the mixed resin No. 2 (Experiment No. 31) cannot obtain the target pre-expanded particles having an expansion ratio of 16 cc / g. LD with a resin density of less than 0.940 g / cm ³
What was obtained by manufacturing from a mixed resin of / LL / HD2 (Experiment No. 32 to 33) was a foaming ratio of 16 cc / g, 33 c.
Although the target pre-expanded particles of c / g can be obtained, the temperature range suitable for molding and molding is narrow, and the compression strength of the obtained molded product is low,
It turns out that the object of the present invention cannot be achieved.

Example 3 In this experiment, a specific four-component mixed resin was used as a raw material resin to be the pre-expanded particles in the present invention, and a low foaming process plus four expansion processes were performed to obtain good quality. It is intended to prove that pre-expanded particles having an expansion ratio of 60 cc / g can be obtained. The following experiment is performed in accordance with the experiment No. Using the pre-expanded particles having an expansion ratio of 33 cc / g of 25, the fourth expansion was performed based on the method for producing the pre-expanded particles described above, and the expansion ratio was 60 cc / g.
g of pre-expanded particles were produced. The obtained pre-expanded particles were good quality expanded particles having a closed cell ratio of 97% and an average cell diameter of 0.52 mm. (Additional test example-1) The experiment here is performed in Japanese Examined Patent Publication No. 60-1004.
These are additional tests and reference comparative tests of the examples disclosed in Japanese Patent Publication No. The resin used for reference is Japanese Patent Publication Sho 60-1.
The HD shown in Japanese Patent Publication No. 0048 was partially added.

The resins shown in Table 7 were melt-kneaded using a 93 mm twin-screw extruder, attached to the tip of the extruder and extruded in a strand form from a die, and cooled and cut to produce resin particles. 100 parts by weight of the resin particles shown in Table 7 in the pressure container,
25 parts by weight of dichlorodifluoromethane as a foaming agent, 300 parts by weight of water, and 0.5 parts by weight of finely divided aluminum oxide as a dispersant are contained, and each predetermined temperature (90 to 150 ° C.) is raised under stirring, Adjust the pressure in the pressure vessel to 10
While holding at 50 kg / cm ² G, one end of the container was opened, and the resin particles and warm water were simultaneously released into the atmosphere to foam, that is, the experiment N of Table 7 was performed by the flash foaming method.
o. Foaming ratio 16cc / g and 33cc / g
Various pre-expanded particles were obtained. The foaming temperature in each experiment at this time was carried out at the temperature shown below. Experiment No. I is 121
° C. Experiment No. B is 120 ℃. Experiment No. Ha is 119
° C. Experiment No. D is 115 ° C. Experiment No. E 114
° C. Experiment No. F is 126 ℃. Experiment No. Is 125
° C. Experiment No. The temperature is 120 ° C.

Next, according to the method for producing pre-expanded particles by the above-described multi-stage temperature-increased foaming method, a low expansion, a first expansion, and a second expansion so as to match the expansion ratio obtained by the flash expansion method. Go up to the process, foaming ratio 16cc / g
With respect to the pre-expanded particles obtained in 16 cc / g, the pre-expanded particles having a foaming ratio of 33 cc / g were manufactured by further expanding the pre-expanded particles of 16 cc / g. The foaming and expansion temperatures in each experiment at this time were carried out at the following vapor pressure of kg / cm ² G (temperature ° C) which was selected in advance.

[0074]

[Table 1]

With respect to the pre-expanded particles obtained in the above experiment, the expansion ratio, closed cell ratio, average cell diameter, oil resistance, weather resistance-1, 2 and heat resistance-1, 2 were evaluated by the above evaluation methods, and The results are shown in Table 7. Further, for each of the obtained expanded particles, based on the above-mentioned method for producing a molded article, the molding suitability temperature range is set in the molding condition section of Table 7 where the best molded article is obtained. Remolding was performed at the molding temperature, and the obtained molded product was used to evaluate the expansion ratio, flexibility, tear strength, flex fatigue resistance, compression elasticity, and compression strength by the above evaluation methods, and the results are shown in Table 7.

According to the results of Table 7, the experiment No. In the "flash foaming method" of I to H, the density is 0.915 to 0.95.
With LLDPE and HDPE in the range of 0 g / cc, it is possible to obtain pre-expanded particles having an expansion ratio of 16 cc / g and 33 cc / g over almost the entire resin density. The resin density is 0.915 in the "multi-stage temperature rising foaming method"
Even if the area of g / cc or more and less than 0.930 g / cc can be pre-expanded particles having an expansion ratio of 16 cc / g, the resin density is 0.930 g / cc or more and the range of 0.965 g / cc has an expansion ratio of 16 cc. It can be seen that this is a region where the expanded particles of / g cannot be obtained. Furthermore, the resin density is 0.915 g / c
The pre-expanded particles obtained by the "multi-stage temperature-increasing foaming method" from the LL resin of c or more and less than 0.930 g / cc are more than the pre-expanded particles obtained by the "flash foaming method" from the resins of the same density and kind, It can be seen that the in-mold formability is poor. From this fact, it is clear that the pre-expanded particles obtained by the "multi-stage temperature rising foaming method" cannot be said to be high-quality expanded particles that can be formed into a molded product that satisfies practical characteristics.

(Additional test example-2) The experiment here is an additional test example-
Experiment No. 1 (Resin is VI in Table 3, polymer density 0.940 cc / g), the expansion ratio was 9 cc / g, the closed cell ratio was 68%, which was obtained by the first expansion of the manufacturing process.
This is an experiment in which the in-mold moldability was checked for pre-expanded particles having an average cell diameter of 0.25 mm. Molding was carried out based on the above-described method for manufacturing a molded product, and it was examined whether a good molded product could be obtained. As a result, a good molded product was not obtained, and the in-mold moldability was x.

(Additional test example-3) The experiment here is an additional test example-
Experiment No. 1 in Table 7 shows that expanded multi-stage temperature-increasing foaming method in Example 1 could not result in expanded particles having an expansion ratio of 16 cc / g. No. resin (VII in Table 3, polymer density 0.945 cc /
g) It is an experiment to see if the foaming agent in the low foaming step may be replaced with the one used in the flash foaming method for the particles to form expanded particles.

The multi-stage temperature-increased foaming described above except that dichlorodifluoromethane was used as a foaming agent and the resin particles were impregnated with dichlorodifluoromethane for 30 minutes under the conditions of a temperature of 80 ° C. and a pressure of 10 kg / cm ² G. Based on the method of manufacturing pre-expanded particles by the method, low foaming, first expansion,
The pre-expanded particles having an expansion ratio of 16 cc / g were manufactured by performing the second expansion step. Regarding the foaming and expansion temperatures for each experiment, the low foaming temperature was 1.20 kg / cm ² G (123.2 ° C.), and the first expansion temperature was 1 0.25 kg / cm ² G (124
℃), the second expansion temperature is steam pressure 1.25kg / cm
Performed at ² G (124 ° C). As a result, the target pre-expanded particles with an expansion ratio of 16 cc / g could not be obtained.

(Additional test example-4) The experiment here is an additional test example-
Experiment No. 1 in Table 7 shows that expanded multi-stage temperature-increasing foaming method in Example 1 could not result in expanded particles having an expansion ratio of 16 cc / g. Resin shown in Table 3 (VI in Table 3, polymer density 0.940 cc / g)
This is an experiment to see if the resin particles can be heat-treated before the foaming step to expand the heating temperature range suitable for foaming and expansion to form expanded particles.

Experiment No. 7 in Table 7 Resin (V in Table 3)
I) Using a pressure vessel, the particles are dispersed in water in the same manner as in the flash foaming method of additional test example-1, and the temperature is kept at three levels of 120 ° C, 123 ° C and 125 ° C for 30 minutes without adding a foaming agent. After heat treatment, it was cooled to room temperature to obtain three kinds of heat-treated resin particles. The obtained resin particles were subjected to DSC measurement by the method described in the text, and the heat-treated particles at 120 ° C. (experimental No.) were 121 ° C. and 126 ° C. in the melting curve.
The temperature (T50) corresponding to 50% of the total heat of fusion is 122 ° C and 70% of the total heat of fusion.
The temperature (T70) which hits is 125 ° C, and the heat-treated particles at 123 ° C (Experiment No. N) are 122 ° C and 127
Two peak temperatures of ℃, T50 is 121 ℃, T70 is 125 ℃, 125 ℃ heat-treated particles (Experiment No. na), the melting curve is one peak temperature of 127 ℃, T50 is 1
23 ° C., T70 was 125 ° C. Using these heat-treated resin particles, based on the method for producing pre-expanded particles by the multistage temperature rising foaming method described above, low foaming,
Expand to the first expansion and the second expansion process to obtain a foaming ratio of 16
Pre-expanded particles of cc / g were produced. The foaming and expansion temperatures in each experiment at this time were carried out at the following vapor pressure of kg / cm ² G (temperature ° C), which was selected in advance.

[0082]

[Table 2]

As a result, 120 ° C. heat treated particles (Experiment N
o. And the 125 ° C. heat-treated particles (Experiment No. NA), pre-expanded particles having a target expansion ratio of 16 cc / g could not be obtained. Pre-expanded particles having an expansion ratio of 16 cc / g, a closed cell ratio of 72%, and an average cell diameter of 0.35 mm were obtained from the 123 ° C. heat-treated particles (Experiment No. N). The pre-expanded particles were molded according to the method for producing a molded article described above, and it was examined whether a good molded article could be obtained. As a result, a good molded product was not obtained, and the in-mold moldability was x.

[0084]

[Table 3]

[0085]

[Table 4]

[0086]

[Table 5]

[0087]

[Table 6]

[0088]

[Table 7]

[0089]

EFFECTS OF THE INVENTION According to the present invention, by having the above-mentioned constitution, non-crosslinked pre-expanded particles of high density polyethylene resin having a resin density of 0.940 to 0.952 g / cm ³ can be easily obtained. The "multi-stage temperature rising foaming method" was completed. In addition, the advantage that the transportation and storage costs can be greatly reduced can be utilized, and the obtained pre-expanded particles have higher basic properties (eg rigidity, compressive strength) and have a wider temperature range suitable for molding. Therefore, there is an effect that, for example, the load receiving area can be reduced, the foam wall thickness can be reduced, or a highly foamed foamed molded product can be easily produced without impairing the cushioning characteristics. Therefore, the present invention can contribute to the overall cost reduction of the cushioning material (foam molded article).

[Brief description of drawings]

FIG. 1 is an experimental diagram, and is a diagram of a melting endotherm curve measured by a differential scanning calorimeter (DSC) of a raw material resin once heated to a foaming temperature and cooled.

FIG. 2 is a diagram of a melting endotherm curve measured by a differential scanning calorimeter (DSC) of a raw material resin after being once heated to a foaming temperature and cooled, which is an experimental diagram similar to FIG.

FIG. 3 is a diagram of a melting endotherm curve measured by a differential scanning calorimeter (DSC) of a raw material resin after being once heated to a foaming temperature and cooled, which is an experimental diagram similar to FIG.

FIG. 4 is a diagram of a melting endotherm curve measured by a differential scanning calorimeter (DSC) of a raw material resin after being once heated to a foaming temperature and cooled, which is an experimental diagram similar to FIG. 1.

FIG. 5 is a diagram of a melting endotherm curve measured by a differential scanning calorimeter (DSC) of a raw material resin after being once heated to a foaming temperature and cooled, which is an experimental diagram similar to FIG. 1.

FIG. 6 is a diagram of a melting endotherm curve measured by a differential scanning calorimeter (DSC) of a raw material resin after being once heated to a foaming temperature and cooled in an experimental diagram similar to FIG.

FIG. 7 is a technical explanatory view by increasing the resin density.

FIG. 8 is a perspective view of a molded body for explaining a mold (a state in which a mold cavity is thick and thin) used for evaluation of the present invention.

FIG. 9 is a schematic plan view of a vapor inflow member arranged on the surface of a mold.

Claims (2)

[Claims] 1. A method for producing non-crosslinked pre-expanded polyethylene resin particles, which comprises using a polyethylene resin as a raw material resin and impregnating the resin particles with a foaming agent to foam the resin particles. A method for producing non-crosslinked pre-expanded particles of polyethylene resin, which comprises: (1) The raw material resin has a density of 0.920 to 0.
30 to 50% by weight of a high-pressure low-density polyethylene resin having a melting point (mLD) of 108 to 118 ° C. of 930 g / cm ³ .
Density 0.916 to 0.928 g / cm ³ , melting point (mL
L) 5 to 30% by weight of linear low-density polyethylene resin having a temperature of 118 to 123 ° C. and a density of 0.955 to 0.970 g /
cm ^3, and a melting point (mHD2) 128~135 20~45 wt% of linear high density polyethylene resins ° C., density 0.
940 to 0.954 g / cm ³ and a linear high-density polyethylene resin having a melting point (mHD1) in the range of [(mHD2 + mLL) ÷ 2] ± 2 ° C. of 10 to 35% by weight and consisting of the four components. Density of mixed resin is 0.940
Use a mixed resin that is ˜0.952 g / cm ³ . (2) When the resin particles are impregnated with the foaming agent and foamed, the resin particles are impregnated with the foaming agent and heated to form low foamed particles having an expansion ratio of 1.5 to 3.5 cc / g. , And then impregnating a foaming agent in the bubbles of the low-expanded particles,
Use a multi-stage temperature-rising foaming method in which this is heated to form expanded particles having a higher expansion ratio. 2. The step of impregnating the foaming agent into the cells of the low-expanded particles and heating this to obtain expanded particles having a higher expansion ratio is repeated 2 to 4 times to obtain an expansion ratio of 6 to 60 cc /
The method for producing pre-expanded non-crosslinked polyethylene resin particles according to claim 1, wherein the expanded particles are g.