JPH10324764A - Production of polyolefin-based resin preexpanded particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for production by which mutual fusion of expanded particles and a rise in open-cell ratio of preexpanded particles are simultaneously prevented to increase the expansion efficiency and polyolefin-based resin preexpanded particles having a high expansion ratio can be produced. SOLUTION: The relationship between a temperature for thermally expanding expanded particles and the amount of a fusion preventing agent sticking to the surfaces of the polyolefin-based resin expanded particles is represented by the formula (t)-TV<=49.1C-27.0 [(t) is the temperature for the thermally expanding the expanded particles; C is the amount of the fusion preventing agent sticking to the surfaces of the polyolefin-based resin expanded particles; TV is the saddle part temperature between the peaks indicating two melting points in a differential scanning calorimetry(DSC) curve obtained by the DSC] and (t) is further a temperature range represented by the formula TL-30<=(t)<=TV (TV is the same as that described above; TL is the melting point on the low-temperature side in the two melting points) in a method for imparting expandability to the polyolefin-based resin expanded particles having a crystal structure manifesting the two melting point in the DSC curve and thermally expanding the expanded particles having the expandability imparted thereto.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing pre-expanded polyolefin resin particles. More particularly, the present invention relates to a method for producing pre-expanded polyolefin resin particles which can be suitably used as a raw material of an in-mold foam molded article.

[0002]

2. Description of the Related Art Conventionally, in the case of producing pre-expanded polyolefin resin particles, the resin particles are dispersed in an aqueous dispersion medium together with a dispersant in a closed vessel, and a volatile foaming agent is introduced. Is heated to a temperature equal to or higher than the softening point temperature of the polyolefin resin, and discharged into an atmosphere at a pressure lower than the internal pressure of the closed container, to produce expanded polyolefin resin particles.

Further, for example, a method for producing pre-expanded polyolefin resin particles having a special crystal structure and exhibiting two melting points in a DSC curve obtained by differential scanning calorimetry using the above method (for example, JP-A-59-176336)
JP, JP-A-63-183832, etc.) and further, by imparting foaming ability to the polyolefin resin pre-expanded particles having the special crystal structure and then heating, while maintaining the closed cell structure, Methods for improving the expansion ratio are already known (JP-A-60-23428, JP-A-60-90228).

Japanese Patent Application Laid-Open No. Sho 60-23428 discloses that
Expanded into non-crosslinked propylene-based random copolymer pre-expanded particles having a specific expansion ratio and a range of the number of cells, and having a crystal structure in which a DSC curve shows a high-temperature peak at a higher temperature side than a unique peak inherent to the base resin. A method for obtaining pre-expanded particles having a higher expansion ratio than the original expansion ratio by heating and foaming after imparting the function is disclosed.

[0005] Also, Japanese Patent Application Laid-Open No. Sho 60-90228 discloses, for example, Japanese Patent Application Laid-Open No. 59-176336,
Polypropylene-based resin pre-expanded particles having a special crystal structure similar to those described in JP-A-63-183832, etc., having an internal pressure reduction rate coefficient k of k ≦ 0.30. And the pre-expanded particles in a closed container are subjected to the following formula: Tm-65 <T <Tm-3
0 (where Tm represents the melting end temperature of the base resin), and one end of the container is released by heating and holding at a temperature T (° C.), and the pre-expanded particles are placed in an atmosphere at a lower pressure than in the container. And a step of releasing.

[0006] However, the techniques in these methods are all polypropylene-based resins, especially ethylene-based resins.
It relates to a propylene random copolymer and does not disclose any technique when another polyolefin resin is used.

[0007] Regarding the heating temperature, usually, preferably 0.8 to 1.5 kg / cm ² (G) of steam (11
6 to 127 ° C.) or a statement that hot air of 100 ° C. or higher is used (Japanese Patent Laid-Open No. 23428/1985), or the formula:
The description of heating at a temperature T (° C.) represented by Tm−65 <T <Tm−30 (where Tm represents the melting end temperature of the base resin) (JP-A-60-90228) However, there is no disclosure of a technique for using pre-expanded particles having a special crystal structure and achieving the object by associating the crystal properties of the pre-expanded particles with the heating temperature.

Further, when the polyolefin resin foamed particles are heated and foamed, if the heating temperature is too high, the open cell ratio of the obtained pre-foamed particles increases, and the pre-foamed particles are used in a mold. After molding,
It is assumed that the mechanical strength of the obtained molded article is significantly reduced, or that the foamed particles are mutually fused to each other, which causes defective filling when supplying the foamed particles to a molding machine. The phenomenon is also mentioned in the above publication.

Therefore, the present inventors have proposed that the above Tm = 157
C. An ethylene-propylene random copolymer at a temperature of .degree. C. was used as a base resin, and the foamed particles having the special crystal structure were subjected to sufficient washing with water and an acidic aqueous solution after production (expansion ratio 11.3 times, average Using a cell diameter of 300 μm and an internal pressure reduction rate coefficient k = 0.15), a steam pressure of 1.5 kg
When foaming was carried out by heating with water vapor at a rate of about 126 ° C./cm ² (G) (about 126 ° C.), pre-expanded particles having a high expansion ratio and a closed-cell structure could be obtained. However, mutual fusion of the foamed particles occurred, resulting in poor filling of the foamed particles during molding.

In the case of producing pre-expanded particles by using the heating expansion method, one of the effective means for increasing the expansion ratio of the obtained pre-expanded particles is to increase the heating temperature,
While it is conceivable to increase the internal pressure of the foamed particles and soften the resin layer on the surface of the foamed particles, if the mutual fusion of the foamed particles occurs as described above, the heating temperature can be increased substantially further. Therefore, the expansion ratio of the obtained pre-expanded particles cannot be increased.

On the other hand, the pre-expanded particles having the special crystal structure are charged into a molding machine and heated and fused with steam.
In a method for producing a polyolefin-based resin foam molded article that can obtain a foam molded article having a desired shape, it is known that one of the factors governing the mold fusion property is the amount of deposits on the surface of the pre-expanded particles. (For example, Japanese Patent Application Laid-Open No. 4-578
No. 38).

That is, polyolefin resin particles are dispersed in an aqueous dispersion medium in a closed container, a volatile foaming agent is introduced, and the resin particles are heated to a temperature higher than the softening point of the polyolefin resin. In a method of producing expanded polyolefin resin particles by releasing into an atmosphere at a pressure lower than the internal pressure of a closed container, an inorganic powder called a dispersant or an anti-fusion agent is added together with the polyolefin resin particles, and the polyolefin resin is added. By adhering to the surface of the resin particles, preventing mutual fusion of the resin particles in the aqueous dispersion medium, and washing and removing the surface deposits during or after the production of the pre-expanded particles, thereby improving the molding fusing property. It is a way to let.

[0013] For example, in the method described in JP-A-4-57838, 100 parts (parts by weight, hereinafter the same) of ethylene-propylene random copolymer pellets are mixed with 3 parts of powdery tribasic calcium phosphate as a dispersant and By adding 0.12 parts of sodium n-paraffin sulfonate and changing the washing method immediately after the generation of the pre-expanded particles, the amount of deposits (mainly tricalcium phosphate) on the surface of the pre-expanded particles is changed. However, if the amount of such deposits is more than 3300 ppm,
The fusing property of the molded article is remarkably reduced, and the fusing rate of the molded article is zero.
% Is pointed out in such a gazette.

[0014]

Therefore, the present inventors can prevent or suppress the mutual fusion of the foamed particles during the heat foaming depending on the amount of the deposit on the surface of the pre-expanded particles. The amount of deposits on the surface of the raw material expanded particles was determined under exactly the same conditions as when the expanded particles were mutually fused at a steam pressure of 1.5 kg / cm ² (G) during the heat expansion. A heating foaming experiment was performed when the amount was increased, and as a result, the steam pressure was increased to 3 kg / cm ² (G) (= 1).
(43 ° C.), it was found that mutual fusion of the foamed particles did not occur.

Other polyolefins such as ethylene-propylene random copolymers, ethylene-α-olefin copolymers, and resin compositions obtained by adding an ethylene ionomer to the ethylene-α-olefin copolymer having different melting end temperatures. The same experiment as described above was carried out for the base resin or its composition. As a result, at a temperature lower than T _L -30 (° C.) with respect to the lower melting point T _L of the two melting points of the pre-expanded particles as the raw material, the improvement in the expansion ratio due to the heat expansion is extremely small. At temperatures above the saddle temperature T _V (° C.) between the two melting peaks,
Irrespective of the melting end temperature of the base resin (composition) or the amount of deposits on the surface of the raw foamed particles, mutual fusion of the foamed particles occurs or open foam of the pre-foamed particles obtained as a result of heating and foaming Rate was 20% or more, and it was found that it was difficult to maintain good moldability for these reasons.

Further, in a temperature range of T _L -30 (° C.) or more and T _V (° C.) or less, the amount of deposits on the surface of the foamed particles and the heating foaming temperature t at which the foamed particles are mutually fused are heated. (° C.)
Surprisingly, even when the expanded particles of any polyolefin resin, wherein: t-T _v upper limit of temperature represented by (at such temperature above occurs mutual fusion bonding of the foamed particles) and foamed It has been found that there is a linear relationship between the amount of the anti-fusing agent attached to the particle surface and the present invention has been completed.

The present invention has been made on the basis of the above-described findings, and uses the expanded polyolefin resin particles having the above-mentioned special crystal structure, and does not cause the fusion of the expanded particles to each other by the heating and foaming method. It is an object of the present invention to provide a method capable of obtaining polyolefin resin pre-expanded particles having a high expansion ratio while maintaining independence.

[0018]

SUMMARY OF THE INVENTION The present invention relates to a foamed polyolefin resin particle having a crystal structure exhibiting two melting points in a DSC curve obtained by differential scanning calorimetry. In the method for producing polyolefin-based resin pre-expanded particles in which the particles are heated and expanded, the relationship between the temperature at which the particles are heated and expanded and the amount of the anti-fusing agent attached to the surface of the expanded polyolefin-based resin particles is represented by formula (I): t -T _V ≤49.1C-27.0 (I) (where, t is the temperature for heating and foaming (° C.), C is the amount (phr) of the anti-fusing agent attached to the surface of the polyolefin resin foam particles, T _V is represented by the saddle temperature (° C.) between two peaks indicating the melting points in the DSC curve), and the temperature for foaming by heating is represented by the formula (II): T _L− 30 ≦ t ≦ T _V (II) (Where Temperature for heating and foaming, T _V is saddle temperature between peaks showing two melting points in a DSC curve (℃) is, T
_L is a temperature range represented by a lower melting point (° C.) of the two melting points), a method for producing polyolefin resin pre-expanded particles, wherein the surface of the polyolefin resin expanded particles is A method for producing the polyolefin-based resin pre-expanded particles wherein the amount of the adhered anti-fusing agent is 0.001 to 0.3 phr, and the polyolefin-based agent wherein the anti-fusing agent is mainly composed of tricalcium phosphate The present invention relates to a method for producing resin pre-expanded particles.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the method for producing polyolefin resin pre-expanded particles according to the present invention comprises foaming polyolefin resin expanded particles having a crystal structure showing two melting points in a DSC curve obtained by differential scanning calorimetry. In the method of heating and foaming the foamed particles to which the foaming ability has been imparted, the relationship between the temperature at which the foaming is performed and the amount of the anti-fusing agent attached to the surface of the polyolefin resin foamed particles is represented by the following formula. (I): t−T _V ≦ 49.1C-27.0 (I) (where, t is the temperature (° C.) at which the foam is heated and foamed, and C is the fusion-preventing agent attached to the surface of the polyolefin resin foamed particles. The amount (phr) and T _V are represented by the saddle temperature (° C.) between two peaks indicating the melting points in the DSC curve), and the temperature at which foaming is carried out by heating is represented by the formula (II): _TL− 30 ≦ t ≦ T _V II) (wherein, t is the temperature for heating foam, T _V is saddle temperature between peaks showing two melting points in a DSC curve (° C.), T
_L is a temperature range represented by the lower melting point (° C.) of the two melting points.

In the present invention, the differential scanning calorimetry is described in, for example, JP-A-60-23428,
The crystallization characteristics of the expanded particles are measured by raising the temperature to 220 ° C. at a rate of 10 ° C./min using a differential scanning calorimeter in the same manner as disclosed in, for example, Japanese Patent Application No. 0-90228.

In the polyolefin resin foam particles used in the present invention, two endothermic peaks (melting points) accompanying crystallization appear in the DSC curve obtained by the differential scanning calorimetry, for example, as shown in the graph of FIG. Of these two peaks, the peak (melting point) on the low temperature side is represented by T
_L (° C) (symbol α in Fig. 2), peak on high temperature side (melting point)
When the T _H (℃) (symbols in Figure 2 beta), normally, the temperature difference T _H -T _L between the two melting points is about 5 to 20 ° C.,
As shown in FIG. 2, these two peaks together form a horse saddle-like shape. In this saddle, D
The SC curve has another extreme value at the position closest to the heat radiation side. In the present invention, this temperature is defined as the saddle portion temperature T.
_V (° C.) (symbol γ in FIG. 2).

The expanded polyolefin resin particles having the specific crystal structure as described above can be produced by expanding the resin particles for expanding the polyolefin resin with a blowing agent.

Examples of the polyolefin resin include propylene resins such as polypropylene, ethylene-propylene random copolymer, ethylene-propylene block copolymer, ethylene-propylene-α-olefin terpolymer; linear low-density polyethylene; Ethylene resins such as low-density polyethylene and high-density polyethylene are used. However, in order to maintain the mechanical strength of the molded article using the pre-expanded particles, in the differential scanning calorimetry of the expanded particles subjected to heat expansion, 2 Endotherm of the whole peak including two melting points is 30 J / g or more, especially 50 J / g
Those showing the crystallinity as described above are preferable. Also,
In consideration of the balance of physical properties of the molded body other than the mechanical strength and the fusing property at the time of molding, a wide suitable range, etc., ethylene-propylene random copolymer and linear low-density polyethylene are particularly preferably used. You.

The polyolefin resin contains a hydrophilic inorganic substance and a hydrophilic organic compound as a foam nucleating agent within a range that does not significantly impair the physical properties of the obtained expanded particles, pre-expanded particles, and molded article. be able to.

As will be described later, by adding water and / or alcohol to the foamed particles at the time of foaming by heating and using them as a foaming aid, the foaming efficiency by heating is further improved. Since these compounds are water-soluble compounds, the inclusion of these hydrophilic substances makes it easier to include water and / or alcohol as a foaming aid in the foamed particles.

Examples of the hydrophilic inorganic substance include talc, silica, borax, sodium phosphate and the like. Examples of the hydrophilic organic compound include a water-absorbing polymer such as cross-linked sodium polyacrylate, and an ethylene ionomer. The addition amount of these hydrophilic substances is preferably about 0.001 to 20 parts based on 100 parts of the polyolefin resin.

In order to obtain polyolefin resin foaming resin particles, for example, the above-mentioned hydrophilic substance or the like is mixed with a polyolefin resin, and the mixture is melt-kneaded with a single-screw or twin-screw extruder.

Next, a foaming agent and an anti-fusing agent are blended with the foaming resin particles, and the resulting mixture is supplied into a closed container and foamed under appropriate conditions, whereby the specific crystal structure as described above is obtained. Thus, foamed polyolefin resin particles having an anti-fusing agent adhered to the surface thereof are obtained.

As the foaming agent, for example, a foaming agent used for imparting foaming ability to polyolefin resin foam particles as described later can be used.
The addition amount may be appropriately adjusted so that the polyolefin-based resin expanded particles have a desired expansion ratio. For example, it is preferably about 0.1 to 30 parts based on 100 parts of the expanded resin particles.

As the anti-fusing agent, any substance conventionally used as a dispersing agent or an anti-fusing agent can be used. For example, finely divided aluminum oxide, tribasic calcium phosphate, calcium carbonate, magnesium carbonate, Kaolin, bentonite and the like can be mentioned, and these can be used alone or in combination of two or more.
Among these, tricalcium phosphate is particularly preferred because of its high fusion-preventing effect. The amount of the anti-fusing agent to be added may be adjusted so that the amount of the anti-fusing agent attached to the surface of the expanded polyolefin resin particles is in the range described below.

The foaming resin particles may appropriately contain a dispersing aid such as sodium n-paraffin sulfonate, sodium dodecylbenzene sulfonate, benzalkonium chloride, or alkyltrimethyl ammonium chloride.

The amount of the anti-fusing agent adhered to the surface of the polyolefin resin expanded particles thus obtained is determined in order to sufficiently exhibit the effect of preventing the mutual fusion of the expanded particles in the temperature range suitable for the heat expansion. It is desirable that the pressure is 0.001 phr or more, preferably 0.005 phr or more. Further, the mutual fusion of the foamed particles during the heating and foaming can be almost completely prevented. In order to eliminate the possibility that washing must be performed before molding, since the melt-adhesiveness is significantly reduced, 0.3 phr or less, preferably 0.1 phr or less.
It is desirably 15 phr or less, more preferably 0.13 phr or less.

The DSC curve of the polyolefin-based resin foamed particles usually has a T _L of 90 to 16
0 ℃ about, T _H is about 110~180 ℃, T _V is 95-1
It is preferable that the temperature is about 75 ° C., the expansion ratio is about 2 to 30 times, and the average cell diameter is about 10 to 500 μm.

Next, expandability is imparted to the polyolefin resin expanded particles.

The method for imparting foaming ability is not particularly limited, and is performed by, for example, a conventionally known method.
For example, the foaming is performed by appropriately adjusting the amount of a foaming agent having a boiling point lower than the heating foaming temperature and not dissolving the polyolefin-based resin in the foamed polyolefin resin particles to be subjected to the heat foaming. There are various kinds of such foaming agents. For example, air, nitrogen gas, inorganic gas such as carbon dioxide gas is versatile, has no flammability and toxicity, and is a gas at the time of heating and foaming. It is particularly preferable because the internal pressure of the expanded particles can be easily maintained at a high level. In addition, lower aliphatic hydrocarbons such as propane, butane, isobutane, pentane, isopentane, cyclopentane and the like, which have been widely used in the production of polyolefin resin pre-expanded particles, and halogenated hydrocarbons are also used. It is possible.
Of these, so-called third-generation fluorocarbons, which do not contain chlorine in the molecule, are preferred among halogenated hydrocarbons, especially in view of the problem of destruction of the ozone layer. The amount of the foaming agent is not particularly limited, but is preferably adjusted so that the internal pressure of the foamed particles during normal heat foaming is about 0.1 to 30 kg / cm ² (G).

Further, in the present invention, water and / or alcohol are preferably used because they have a low vapor pressure during heating and foaming, but when used as a foaming aid, the foaming efficiency is further increased.

Next, the expanded particles provided with the expandability as described above are heated to produce polyolefin resin pre-expanded particles.

As a method for foaming by heating, for example, a method using hot air or steam can be adopted. For example, as disclosed in JP-A-59-133233, a method using steam is used. It is particularly preferable because the supply of heat to the particles is quick and the productivity is improved. When steam is used, a heating time of about 1 minute is usually sufficient.

In the production method of the present invention, the relationship between the temperature at which the foamed particles provided with the foaming ability is heated and foamed and the amount of the anti-fusing agent attached to the surface of the polyolefin resin foamed particles, a temperature of foaming, T _V,
There is a great feature in the relationship with _TL .

As described above, the relationship between the temperature at which the foamed particles provided with the foaming ability is heated and foamed and the amount of the anti-fusing agent adhered to the surface of the polyolefin resin foamed particles is represented by the formula (I): t -T _V ≤49.1C-27.0 (I) (where, t is the temperature for heating and foaming (° C.), C is the amount (phr) of the anti-fusing agent attached to the surface of the polyolefin resin foam particles, T _V is the saddle temperature (° C.) between two peaks indicating the melting points in the DSC curve), where t is expressed by the formula (II): _TL− 30 ≦ t ≦ T _V ( II) where T _V is the same as above, and T _L is the lower melting point (° C.) of the two melting points.

The temperature t for the heating and foaming is _TL- 30.
(° C.) or more, preferably _TL- 25 (° C.) or more,
And it is below T _V (° C.), preferably below T _V -2 (° C.).

When the temperature t is lower than the lower limit, the heating temperature is too low, so that the resin layer forming the foamed particles is hard, the foaming efficiency ε is low, and the ratio of the foaming ratio before and after the heating and foaming is increased. Is not preferred.

Here, the foaming efficiency ε is calculated by the following equation (II)
I):

[0044]

(Equation 1)

(Where K ₀ is the expansion ratio of the expanded particles before thermal expansion, K is the expansion ratio of the pre-expanded particles after thermal expansion, P
₀ is the internal pressure of the foamed particles at room temperature (23 ° C.) [atm (abs)] immediately before heating and foaming, and T is the heating foaming temperature (t + 27).
3.2 (° C.)), and _Tr is given at room temperature (= 23 ° C.) at the time of _PO measurement.

That is, when the expansion ratio before and after the heating and foaming does not change (K _O = K), ε = 0, and the temperature converted value of the applied internal pressure of the expanded particles until the pressure becomes the atmospheric pressure due to the heating and foaming. If the volume expansion is equal to the volume expansion of the expanded beads before and after the heating expansion, ε = 1. Therefore, when an action of a foaming aid such as water, steam, or alcohol is added, ε> 1 may be satisfied.

The heating foaming temperature is low, and t <(T _L− 30)
In the case of, the foaming efficiency was low, and ε <0.1.
Therefore, according to the above formula (III), if it is desired to increase K, it is necessary to increase P _0. For this purpose, it is necessary to increase the pressure at which the foaming ability is applied or to increase the foaming ability. The time to do this must be lengthened, which is not desirable.

If t exceeds the upper limit value, mutual fusion and / or open cell formation of the expanded particles occur.
Not preferred.

As described above, when the temperature t for foaming by heating is within the temperature range represented by the formula (II), t−T
_A linear relationship between the upper limit temperature (° C.) of _V and the amount C (phr) of the anti-fusing agent attached to the surface of the expanded polyolefin resin particles, that is, the above formula (I): t−T _V ≦ 49.1C The relationship represented by −27.0 (I) holds.

Once the amount C of the anti-fusing agent attached to the surface of a particular expanded particle is determined, the determined C and T _V are determined.
, The upper limit of the temperature t that enables good heating and foaming without causing mutual fusion of the foamed particles is uniquely determined.
The upper limit of the temperature t is set, for example, by preparing several types of expanded particles having different _TV and C, and for each expanded particle,
It is determined by conducting a heating foaming evaluation experiment at several heating temperatures.

FIG. 1 shows the upper limit temperature t-T _V (° C.)
The relationship with the amount C (phr) of the anti-fusing agent is shown. As apparent from FIG. 1, t-T _V is in C and linear relationship, Figure 1
In the lower right region surrounded by the open cell critical line A and the fusion critical line B, mutual fusion did not occur. This was a preferable region, and conversely, mutual fusion occurred in the upper left region. In this case, t-T _V> 0 and t-T _V <49.1C-2
In the region of 7.0 (the region above the open cell critical line A), mutual fusion of the expanded particles did not occur, but the open cell ratio of the obtained pre-expanded particles exceeded 20%.

As described above, the formulas (I) and (II)
By adjusting the amount of the anti-fusing agent to be adhered to the surface of the polyolefin-based resin foamed particles and the temperature at which the foamed particles provided with the foaming ability are heated and foamed so as to satisfy the condition represented by the above, mutual fusion of the foamed particles is performed. Does not occur, and polyolefin-based resin pre-expanded particles having a high expansion ratio can be obtained while maintaining the independence of the cells.

[0053]

Next, the method for producing the pre-expanded polyolefin resin particles of the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to only these Examples.

About the melting point and the melting end temperature of the polyolefin resin (base resin) used in the following Examples and Comparative Examples, about 1 to 10 mg of base resin particles were precisely weighed, and a differential scanning calorimeter (Seiko) was used. SS manufactured by Electronic Industry Co., Ltd.
C5200), the endothermic peak obtained by raising the temperature from room temperature to 220 ° C. at a rate of 10 ° C./min was taken as the melting point. The melting end temperature was measured according to the method described in JP-A-60-23428.

Example 1 and Comparative Examples 1 to 4 Ethylene-propylene random copolymer (melting point: 137 ° C., melting end temperature: 157) as polyolefin resin
C)) to produce resin particles for foaming having a particle weight of about 1.8 mg with a single screw extruder (50 mmφ, L / D = 3). At this time, 0.005 phr of talc was mixed as a foam nucleating agent.

100 parts of the obtained resin particles for foaming were mixed with the first
Are supplied together with 300 parts of water, 1.4 parts of tribasic calcium phosphate as an anti-fusing agent and 0.03 parts of sodium n-paraffin sulfonate as a dispersing aid, at a foaming temperature of 138 ° C and a foaming pressure of 17 kg /. Under a condition of cm ² (G), the mixture was foamed through a circular orifice having a diameter of 4 mm to obtain polyolefin resin foamed particles. At this time, 13 parts of isobutane was used as a foaming agent.

The expansion ratio and average cell diameter of the obtained expanded polyolefin resin particles were examined in accordance with the following methods. As a result, the polyolefin resin foamed particles were foamed particles having an expansion ratio of 11.3 times and an average cell diameter of 300 μm and having a closed cell structure.

The polyolefin-based resin foamed particles were obtained by using a differential scanning calorimeter (manufactured by Seiko Denshi Kogyo KK, SS
C5200) has a special crystal structure showing two melting points in a DSC curve by differential scanning calorimetry using
_L is 136.8 ° C., T _V is 149.4 ° C., T _H is 156.
7 ° C.

Next, the foamed polyolefin resin particles were sufficiently washed with an aqueous hydrochloric acid solution of pH 3, washed with water, and dried. The amount of the anti-fusing agent attached to the surface of the dried polyolefin resin foam particles was measured according to the method described below. As a result, the amount of the anti-fusing agent was 0.05 phr. Then, the expanded particles are
5kg / cm
² (G) and left at room temperature for about 24 hours to give foaming ability. After taking out from the second closed container, the internal pressure decreasing rate coefficient was calculated to be 0.15, and the internal pressure at 23 ° C. of the expanded particles provided with the expandability immediately before the heat expansion was 3.9 a.
tm (abs).

Further, after the foamed particles provided with the foaming ability were supplied into a third hermetically sealed container, they were subjected to heating and foaming under the conditions shown in Table 1 to obtain polyolefin-based resin pre-foamed particles.

As the characteristics of the obtained polyolefin resin pre-expanded particles, the expansion ratio, expansion efficiency, open cell ratio and mutual fusion were examined in accordance with the following methods. Table 1 shows the results.

[Expanded Polyolefin Resin Particles] (Expansion Ratio (K ₀ )) Approximately 2 g of expanded particles were precisely weighed, the volume was measured by a submersion method, and the true specific gravity of the expanded particles was determined.
It was determined by dividing the true specific gravity of the resin (composition) by the true specific gravity of the foamed particles.

(Average cell diameter) The cross section of the expanded particles was determined by microscopic observation.

(Amount of Anti-Fusing Agent (Tricalcium Phosphate) Attached to Surface of Expanded Particles (C)) An aqueous solution containing 0.022% by weight of ammonium metavanadate, 0.54% by weight of ammonium molybdate and 3% by weight of nitric acid (Colorimetric liquid) 50.0 ml and W (g) expanded particles were placed in a conical beaker, stirred for 1 minute, and then left for 10 minutes. The obtained liquid phase was placed in a quartz cell having an optical path length of 1.0 cm, and the absorbance A at 410 nm was measured with a spectrophotometer.

Using the absorbance coefficient μ (g / L · cm) of the tricalcium phosphate at 410 nm, which was measured in advance for the same colorimetric liquid, the amount C (phr ).

[0066]

(Equation 2)

[Pre-expanded Polyolefin Resin Particles] (Expansion Ratio (K)) The expansion ratio (K ₀ ) was determined in the same manner as the expansion ratio (K ₀ ) of the polyolefin resin expanded particles.

(Expansion efficiency (ε)) Formula (III):

[0069]

(Equation 3)

(Where K ₀ , K, P ₀ , T and Tr are the same as above).

(Open cell ratio) The closed cell volume of the obtained pre-expanded particles was determined by using an air comparison type hydrometer (manufactured by Tokyo Science Co., Ltd., type 1000), and this was determined by the apparent volume separately determined by the submerged method. The closed cell rate (%) obtained by dividing
It was determined by subtracting from 00.

(Mutual fusion) The obtained pre-expanded particles were visually observed to check for mutual fusion.

Example 2 Comparative Example 3 was repeated except that the addition amount of the anti-fusing agent was 2.5 parts, washing was carried out sufficiently immediately after being discharged from the first closed container, and washing with an aqueous hydrochloric acid solution was not carried out. Similarly, pre-expanded polyolefin resin particles were obtained.

The properties of the obtained polyolefin-based resin pre-expanded particles and the properties of the polyolefin-based resin expanded particles obtained on the way were examined in the same manner as in Example 1. Table 1 shows the results.

Examples 3 to 5 and Comparative Example 5 Ethylene-propylene random copolymer (melting point: 145 ° C., melting end temperature: 161) as polyolefin resin
° C), the amount of talc added was 0.01 phr, and washing with an aqueous hydrochloric acid solution was not performed.
In the same manner as in the above, polyolefin resin pre-expanded particles were obtained. However, the internal pressure at 23 ° C. of the foamed particles to which the foaming ability was imparted immediately before heat foaming was 4.3 atm (abs).

The properties of the obtained polyolefin-based resin pre-expanded particles and the properties of the polyolefin-based resin expanded particles obtained on the way were examined in the same manner as in Example 1. Table 1 shows the results.

Example 6 and Comparative Examples 6 and 7 98% by weight of the ethylene-propylene random copolymer used in Examples 3 to 5 and Comparative Example 5 were used as the polyolefin resin, and Mitsui Dupont Polypropylene was used as the ethylene ionomer. "Himilan # 1707" manufactured by Chemical Company 2
Using 100 parts by weight of a resin mixture containing 100 parts by weight of talc and 1 part of talc, resin particles for foaming were obtained using the same single screw extruder as used in Example 1. The melting point of the obtained resin particles for foaming was 147 ° C, and the melting end temperature was 159 ° C.

Next, when foamed polyolefin resin particles are obtained from the first closed container, water is used as a foaming agent.
Foaming temperature 155 ° C, Foaming pressure 30kg / cm ² (G)
(Pressurized nitrogen gas), except that foamed polyolefin resin particles were obtained in the same manner as in Example 1. The expanded polyolefin resin particles have an expansion ratio of 9.8 times, an average cell diameter of 150 μm, and a T _L of 1 on a DSC curve.
43.5 ℃, T _V was 155.6 ℃.

Next, the foamed polyolefin resin particles are sufficiently washed with a hydrochloric acid aqueous solution having a pH of 1 and then placed in a second closed container, and the internal pressure of the second closed container is increased to 8 kg / cm ² with nitrogen gas. (G) and left for 3 hours in a water bath at 80 ° C. to give foaming ability. The internal pressure reduction rate coefficient of the foamed particles to which the foaming ability has been imparted is 1.7, which is 23 immediately before heating and foaming.
The internal pressure at ° C. was 5.0 atm (abs).

Further, after the foamed particles provided with the foaming ability were supplied into a third closed container, they were heated and foamed under the conditions shown in Table 1 to obtain polyolefin resin pre-foamed particles.

The characteristics of the obtained polyolefin resin pre-expanded particles and the characteristics of the polyolefin resin expanded particles obtained on the way were examined in the same manner as in Example 1. Table 1 shows the results.

Examples 7 to 8 and Comparative Example 8 A linear low-density polyethylene (melting point: 120 ° C., melting end temperature: 132 ° C.) was used as the polyolefin resin.
Resin particles for foaming were obtained in the same manner as in Example 1, except that the amount of talc added was 0.01 phr.

Next, water is used as a foaming agent for foaming in the first closed container, at a foaming temperature of 125 ° C. and a foaming pressure of 35 ° C.
Foamed polyolefin-based resin particles were obtained in the same manner as in Example 1 except that the addition amount of tribasic calcium phosphate as an anti-fusing agent was changed to 4.0 parts at kg / cm ² (G) (air pressurization). .

The foaming ability in the second closed container is obtained by washing the polyolefin resin foam particles without washing.
The internal pressure of the second closed container is increased to 8 kg / cm ² by air pressurization.
(G) and left at room temperature for 18 hours. As a result, the internal pressure decreasing rate coefficient was 0.15, and the internal pressure at 23 ° C. of the expanded particles to which the foaming ability was imparted immediately before heating and foaming was 5.0 atm (abs).

Further, the foamed particles provided with the foaming ability were supplied to a third airtight container, and then heated and foamed under the conditions shown in Table 1 to obtain polyolefin resin pre-foamed particles.

The characteristics of the obtained polyolefin-based resin pre-expanded particles and the characteristics of the polyolefin-based resin expanded particles obtained on the way were examined in the same manner as in Example 1. Table 1 shows the results.

Note that these Examples 7 to 8 and Comparative Example 8
FIG. 2 shows a DSC curve by differential scanning calorimetry of the expanded polyolefin resin particles used in Example 1.

Examples 9 to 11 and Comparative Examples 9 to 10 As the polyolefin resin, 95% by weight of the linear low-density polyethylene used in Examples 7 to 8 and Comparative Example 8
And an ethylene ionomer obtained by adding 0.1 part of talc to 100 parts of a resin mixture composed of 5% by weight of "Himilan # 1856" manufactured by DuPont-Mitsui Polychemicals Co., Ltd. Resin particles for foaming were obtained with the same single screw extruder.

Next, foamed polyolefin-based resin particles were prepared using the foamed resin particles in the same manner as in Examples 7 to 8 and Comparative Example 8, and the expansion ratio was 3.1 times.
Average cell diameter of 160 .mu.m, T _L is 108.6 ° C., T _V is 1
It had a closed cell structure at 18.7 ° C.

Further, the foamed polyolefin-based resin particles were given foaming ability in the same manner as in Examples 7 to 8 and Comparative Example 8, and subjected to heat foaming under the conditions shown in Table 1 to obtain pre-expanded polyolefin-based resin particles. I got it.

The properties of the obtained polyolefin-based resin pre-expanded particles and the properties of the polyolefin-based resin expanded particles obtained on the way were examined in the same manner as in Example 1. Table 1 shows the results.

Table 1 shows that T _L and T _V and t-T _L and t-
T _V is also shown together.

[0093]

[Table 1]

The following can be seen from the results shown in Table 1.

(A) By comparing Example 1 with Comparative Examples 1-4, as in Example 1, t, T _V , T _L and C are represented by the formulas (I) and (II). When all of the relationships are satisfied, the expansion ratio, the expansion efficiency and the open cell ratio are all good, and excellent pre-expanded particles without mutual fusion are obtained. like,
When t, T _V and C do not satisfy the relationship represented by the formula (I), mutual fusion is recognized, and as shown in Comparative Example 4, t, T _V , T _L and C have the formulas ( I) and the formula (I
If none of the relations represented by I) is satisfied, mutual fusion is recognized and the open cell rate becomes extremely high.

When the amount of the anti-fusing agent attached to the surface of the expanded particles is as small as 0.05 phr, mutual fusion of the expanded particles occurs at a relatively low heating temperature. It can be seen that the foaming temperature cannot be increased.

(B) Comparison between Example 2 and Comparative Example 3
As in Example 2, C was increased to 0.49 phr and t,
When T _V , T _L and C satisfy the relations represented by the formulas (I) and (II), the expansion ratio and the expansion efficiency are high, the open cell ratio is low, and the mutual expansion ratio is low. Excellent pre-expanded particles without fusion are obtained.

(C) By comparing Examples 3 to 5 with Comparative Example 5, as in Examples 3 to 5, t, T _V , T _L and C are represented by the formulas (I) and (II). When all of the relationships expressed are satisfied, the expansion ratio, the expansion efficiency and the open cell ratio are all good, and excellent pre-expanded particles free from mutual fusion are obtained. T, T
_{When V} and C do not satisfy the relationship represented by the formula (I), mutual fusion is recognized.

When the amount of the anti-fusing agent attached to the surface of the foamed particles is as large as 0.28 phr, mutual fusion of the foamed particles does not occur until a relatively high foaming temperature is reached. It can be seen that the expansion efficiency and expansion ratio can be increased.

(D) By comparing Example 6 with Comparative Examples 6 and 7, as in Example 6, t, T _V , T _L and C are represented by the formulas (I) and (II). When all of the relationships are satisfied, the expansion ratio, the expansion efficiency and the open cell ratio are all good, and excellent pre-expanded particles without mutual fusion are obtained. , T, T
_{When V} and T _L do not satisfy the relationship represented by the formula (II), the foaming efficiency becomes extremely low.
When t, T _V and C do not satisfy the relationship represented by the formula (I), mutual fusion is recognized.

In the heat foaming, if the amount of the anti-fusing agent is too small, mutual fusion of the foamed particles is likely to occur, so that the range of the suitable heating temperature condition is narrowed.

(E) By comparing Examples 7 and 8 with Comparative Example 8, as shown in Examples 7 and 8, t, T _V , T _L and C are represented by the formulas (I) and (II). When all of the relations are satisfied, the expansion ratio, the expansion efficiency and the open cell ratio are all good, and excellent pre-expanded particles free of mutual fusion are obtained. When the heating temperature is too high and t, T _V , and T _L do not satisfy the relationship represented by the formula (II), the open cell rate becomes extremely high as 41.7%, and the closed cell structure However, it cannot be said that the expanded particles have the following.

As in Examples 7 to 8 and Comparative Example 8, when the amount of the anti-fusing agent is as large as 0.765 phr, the molding fusing property during in-mold molding is reduced. Then, it was sufficiently washed with an acidic aqueous solution so that the amount of the anti-fusing agent at the time of molding in the mold was 0.3 phr or less.

(F) By comparing Examples 9 to 11 and Comparative Examples 9 to 10, as shown in Examples 9 to 11, t, T _V , T _L and C are represented by the formulas (I) and (II). When all of the relationships represented by the formulas (1) and (2) are satisfied, the expansion ratio, the expansion efficiency and the open cell ratio are all good, and excellent pre-expanded particles without mutual fusion are obtained. Examples 9 to 10
As the heating temperature is too high, t, in the case where T _V and T _L does not satisfy the relationship represented by formula (II), Ren'awaritsu is remarkably increased by more than 20%, closed cell structure It cannot be said that the foamed particles have the following.

When the amount of the anti-fusing agent is as large as 0.771 phr as in Examples 9 to 11, mutual fusion of the foamed particles does not occur at each level, and the foaming efficiency is about 0.4 to 0. .
8, it can be seen that the expansion ratio of the pre-expanded particles can be adjusted.

Examples 9 to 11 and Comparative Examples 9-1
If the amount of the anti-fusing agent is as large as 0.771 phr, as in 0, the molding fusing property at the time of in-mold molding is reduced. The amount of the anti-fusing agent at that time was adjusted to 0.3 phr or less.

[0107]

According to the production method of the present invention, the heat foaming efficiency is increased while simultaneously preventing the fusion of the foamed particles during the heat foaming and the increase in the open cell ratio of the pre-expanded particles due to the breakage of the cell membrane. Polyolefin-based resin pre-expanded particles having a high expansion ratio can be produced.

The pre-expanded polyolefin resin particles obtained by the production method of the present invention can be easily molded by a conventionally known molding method, and can be suitably used for applications such as cushioning materials. .

[Brief description of the drawings]

FIG. 1 shows the relationship between the amount (C) of an anti-fusing agent attached to the surface of expanded polyolefin-based resin particles and the upper limit temperature (t-T _V ) at which expanded foamed particles having expanded ability are heated and foamed. It is a drawing.

FIG. 2 shows a DSC of the expanded polyolefin resin particles used in Examples 7 to 8 and Comparative Example 8 by differential scanning calorimetry.
It is a curve.

Claims (3)

[Claims] 1. A polyolefin-based resin obtained by imparting expandability to expanded polyolefin-based resin particles having a crystal structure exhibiting two melting points in a DSC curve obtained by differential scanning calorimetry, and then heating and expanding the expanded particles provided with the expandability. in the method for manufacturing pre-expanded particles, wherein the temperature for heating and foaming, the relationship between the amount of anti-fusing agent adhered to the surface of the polyolefin resin expanded particles has the formula _{(I): t-T V} ≦ 49.1C- 27.0 (I) (where, t is the temperature for foaming by heating (° C.), C is the amount (phr) of the anti-fusing agent attached to the surface of the expanded polyolefin resin particles, and T _V is the two in the DSC curve. expressed in saddle temperatures between peak indicating the melting point (℃) shows a), and the temperature for heating foaming formula _{(II): T L -30 ≦} t ≦ T V (II) ( wherein, t is heat-foamable Temperature, T _V is the saddle temperature (° C.) between the peaks indicating the two melting points in the DSC curve, T
_L is a temperature range represented by the lower melting point (° C.) of the two melting points), wherein the polyolefin resin pre-expanded particles are produced. 2. The method for producing pre-expanded polyolefin resin particles according to claim 1, wherein the amount of the anti-fusing agent attached to the surface of the expanded polyolefin resin particles is 0.001 to 0.3 phr. 3. The method for producing pre-expanded polyolefin resin particles according to claim 1, wherein the anti-fusing agent contains tribasic calcium phosphate as a main component.