JPH08253614A - Synthetic resin composition for foaming, foam molding material and molded foam - Google Patents

Abstract

PURPOSE: To obtain a synthetic resin composition for foaming useful as industrial parts, capable of being in parted with recycling properties, improving expansibility and easily controlling foaming magnifications by blending a thermally decomposable foaming agent with a specific polyolefin. CONSTITUTION: This synthetic resin composition for foaming comprises 95-50wt.% polyolefin having <0.6 long chain branching index (e.g.; branched low density polyethylene, etc.) and 5-50wt.% thermally decomposable foaming agent (e.g.; sodium bicarbonate, etc.). In the component A, e.g. when a polyethylene-based thermoplastic resin is used in the matrix, it is preferable to use a polyolefin having 0.01-20g/10min. melt flow rate(MFR) at 190 deg.C and 2.16kgf, 0.87-0.965(g/cm<3> ) density and 5-40Mw/Mn molecular weight distribution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a foam molding material used for molding various foam molded articles by a chemical foaming method using a chemical foaming agent, a foaming resin composition used for producing the foam molding material, and The present invention relates to a foam obtained by using the foam molding material.

[0002]

2. Description of the Related Art The expansion ratio is 1.1 to 5.0 for many applications including industrial parts and industrial materials such as automobiles and home appliances.
About twice as many foam moldings are used. Among them, a multilayer molded article in which at least one layer among a plurality of layers is formed of a foamed molded article is widely used for the purpose of its unique touch, elasticity, vibration resistance, molding stability and the like. To form a foamed molded article, for example, first, various thermoplastic resins are mixed with a foaming agent and optionally a crosslinking agent according to the intended use of the molded article to prepare a foamed molding material. . Next, the foamed molding material is extruded from a die of various shapes while being molded in an extruder while being heated to a temperature at which the foaming agent contained therein is not decomposed. Then, the obtained molded product is subjected to a crosslinking treatment by heating or ionizing radiation, and then subjected to a heat treatment again to foam the foaming agent to produce a foamed molded product. In addition, it is generally performed in the present molding field to perform molding while foaming the foamed molding material into various shapes while heating at a temperature at which the foaming agent decomposes. Also, depending on the desired foamed molded product,
According to the above method, a foamed sheet is molded, and then the foamed sheet is subjected to vacuum molding, pressure molding or the like to produce a final molded product.

[0003]

However, the conventional method described above has the following problems. When expansion molding such as vacuum molding or pressure molding is performed on the cross-linked foamed molded product as in the above method, since the expandability is low, it is easy to break during molding and pinholes are easily generated. Further, it is difficult to perform molding and foaming at the same time, and the number of manufacturing steps is large. Moreover, the degree of freedom in the shape of the molded product is low, and the selection of the material is likely to be restricted. In particular, the matrix resin must be crosslinkable, which is naturally limited. Furthermore, in order to produce a multilayer molded article,
Each layer must be molded separately, and then they must be laminated and processed, which not only requires a large number of steps, but also has a low degree of freedom in the shape of the molded product and is subject to restrictions on material selection. .

On the other hand, in the method of molding while decomposing the foaming agent, when extruded from the die of the extruder, the foam cells are biased in the die, or the foam cells aggregate to form continuous cells. It is not preferable because the expansion ratio is greatly reduced due to cracking, and it is difficult to obtain a foamed molded product having uniform foam cells. The main reason for this is that in the route from the extruder to the die outlet, back pressure is applied by plasticization inside the extruder, while the die outlet is at normal pressure, so there is a pressure difference between them. Due to That is, the foam cells generated toward the outlet move to the lower pressure side while growing, and are easily coalesced with other foam cells, and the stability of the foam cells is deteriorated and unevenness is likely to occur. Become. In particular, in blow molding, when the pressure in the die fluctuates or the parison is expanded during molding, the pressure drops, and the bubbles expand, especially from the thin portion, and coalesce with other bubbles to form large open cells. Such large bubbles often move to the interface of the molded product and become so-called blisters or avatars, which is a factor that deteriorates the appearance. Therefore, since the stability of the foam cell depends on the melt viscosity of the matrix resin when the foaming agent is thermally decomposed, the molecular weight of the matrix resin can be increased, or it can be molded at a very low temperature using a special molding machine. ,
Attempts have been made to solve the problem by increasing the melt viscosity. However, there is a limit to the stabilization of the foam cells by increasing the melt viscosity due to molding restrictions. Moreover, in such a method, various restrictions are imposed when molding a multilayer structure, and stable molding cannot be performed.

The present invention has been made in order to solve the above-mentioned problems, and enables a high expansion ratio, improves the developability, expands the range of selection of materials, and manufactures foamed molded products having various characteristics. The present invention provides a foam molding material that enables the above, a foaming resin composition contained in the foam molding material, and a foam obtained by using the foam molding material.

[0006]

The foaming resin composition of the present invention comprises a polyolefin 95 having a long chain branching index of less than 0.6.
The resin composition for foaming is characterized by comprising ˜50% by weight and 5 to 50% by weight of a pyrolyzable foaming agent.

The foaming molding material of the present invention comprises a foaming resin composition comprising 95 to 50% by weight of a polyolefin having a long chain branching index of less than 0.6 and 5 to 50% by weight of a pyrolyzable foaming agent, and a long chain. It is characterized by comprising a thermoplastic resin having a branching index of 0.6 to 1.0 (hereinafter referred to as a matrix resin).

The polyolefin having a long chain branching index of less than 0.6 which can be used in the foaming resin composition of the present invention includes branched low density polyethylene, polypropylene having a long chain branching, ethylene propylene rubber, ethylene copolymer. And so on.

Here, the long chain branching index (hereinafter sometimes referred to as g ') is obtained by the following formula, and g'less than 1 means having a long chain branching. g ′ = [A] / [B] where [A] is the intrinsic viscosity of a polyolefin having long chain branching, and [B] is the intrinsic viscosity of a linear polyolefin having the same weight average molecular weight as [A]. . Intrinsic viscosity as the intrinsic viscosity number depends on the size and shape of the polymer molecule to be dissolved, and when comparing a non-linear polymer to a linear polymer with the same weight average molecular weight, the configuration of the non-linear polymer molecule is Shows the rate. Therefore, g'means a measure of the degree of branching of the non-linear polymer. The measuring method of the intrinsic viscosity is described in J. App. Poly. Sci. , 14 2947
-2963 (1970). In addition, the weight average molecular weight of Meconnel is Am.
Lab. , May 1978.
This is because the absolute molecular weight was determined by the "low-angle laser light scattering photometric method" in the paper entitled "Method for determining polymer molecular weight and molecular weight distribution by low-angle laser light scattering" Chain and non-linear polymers were selected and used to measure the degree of branching.

It is necessary that g'is less than 0.6, preferably 0.55 or less, particularly preferably 0.5 to 0.55. When g'is 0.6 or more, the foamed cells cannot be stabilized and the effect of the present invention cannot be obtained.
When g'is less than 0.05, not only is the dispersion in the matrix resin poor, but the appearance of the foamed product as a crosslinked product deteriorates, which is not preferable.

A polyolefin having a long chain branching index of less than 0.6 can be obtained by, for example, devising a catalyst, temperature and pressure in a high pressure polyethylene production process. It can also be obtained by polymerizing with a single-site catalyst, for example, a catalyst system using a dicyclopentadienyl compound / alkoxysilane compound as a cocatalyst. The latter is also possible with polypropylene.

Further, as shown in JP-A-59-93711, introduction of branching into polyethylene or polypropylene by light crosslinking by addition of peroxide, branching into polyethylene or polypropylene by copolymerization of diene monomer. (JP-A-4-103642), introduction of branching into polyethylene or polypropylene by electron beam cross-linking or the like (JP-A-62-121704), and branching into polyolefin by reaction of maleic anhydride grafted polyolefin with a polyfunctional compound. It can be manufactured by introduction or the like.

The polyolefin used for the foaming resin composition varies greatly depending on the thermoplastic resin used for the matrix.
The melt flow rate at 2.degree.
01-20g / 10 minutes, density 0.87-0.965 (g
/ Cm ³ ), and the molecular weight distribution Mw / Mn is preferably in the range of 5-40. In the case of polypropylene, it is 19
The melt flow rate at 0 ° C. and 2.16 kgf is 0.01 to 20 g / 10 minutes, and the molecular weight distribution Mw / Mn is 5.
The thing of the range of -30 is preferable.

The matrix resin referred to here is a material that constitutes the majority of the present foam molding material, and means the resin of the other party with which the foaming resin composition blended with the foaming agent is mixed, for example, 16 in FIG. Is. Here, it is important that the long-chain branching index of the matrix resin is 0.6 to 1.0. When it is less than 0.6, not only is it preferable in terms of cost, but also gel and fish eyes are increased, which is apt to cause perforation, for example, when thermoforming a foamed sheet molded by the system of the present invention, which is not preferable. On the other hand, since the long-chain branching index is an index of 1.0 at the maximum, basically no index exceeds 1.0.

The pyrolyzable foaming agent used in the present invention includes:
Sodium bicarbonate, azodicarboxamide (ADCA), azobisisobutyronitrile, dinitrosopentamethylenetetramine, 4,4-oxybisbenzoesulfonylhydrazide, paratoluenesulfonylacetone hydrazone, citric acid, oxalic acid and the like. To be These thermally decomposable foaming agents may be used alone or in combination of two or more.

In the resin composition for foaming of the present invention, the thermally decomposable foaming agent is preferably 5 to 50% by weight, more preferably 6 to 40% by weight. If it is less than 5% by weight, the amount of the foaming resin composition added to the matrix resin must be increased in order to increase the expansion ratio, and as a result, foam molding tends to be unstable. On the other hand, if it exceeds 50% by weight, the dispersibility of the foaming agent tends to be poor. That is, when the foaming resin composition is kneaded with the matrix resin and molded, it is difficult to form uniform and stable foam cells due to poor dispersion of the foaming agent.

Other additives may be appropriately added to the foaming resin composition. In particular, metal soaps such as zinc stearate and calcium stearate, fatty acids such as stearic acid and 12-hydroxystearic acid, and lubricants such as fatty acid amides such as stearyl amide are preferably added to lower the kneading temperature during extrusion kneading. . The addition amount is preferably in the range of 0.05 to 10% by weight in the foaming resin composition,
More preferably, it is -5% by weight. Further, various foaming aids for controlling the decomposition temperature of the foaming agent may be added.

In the foaming resin composition of the present invention, a polyolefin having a long chain branching index of less than 0.6 and a thermally decomposable foaming agent, or various additives are melted at a temperature not higher than the thermal decomposition temperature of the thermally decomposable foaming agent. It is pelletized after mixing to obtain particles. At this time, the particle diameter is preferably 0.2 to 10 mm, particularly preferably 0.5 to 7 mm. In the case of pellets, the length is the same as the particle diameter, or preferably in the range of 0.5 to 4.5 mm.

It is difficult to produce a molded product from the foaming resin composition of the present invention alone, and when it is mixed with a matrix resin, a foaming molding material that can be used for molding is provided. In this case, only pellets may be mixed (dry blended), but pellets obtained by melting and mixing at a temperature not higher than the thermal decomposition temperature of the thermally decomposable foaming agent and pelletizing can also be used.

Here, the matrix resin has a function of forming a matrix phase in the molded product, and the combination of thermoplastic resin / foaming resin composition is polypropylene (hereinafter, also referred to as PP) / branched low. Density polyethylene (hereinafter also referred to as LDPE), PP / linear low density polyethylene (hereinafter also referred to as LLDPE), PP / linear high density polyethylene (hereinafter also referred to as HDPE),
PP / ethylene / vinyl acetate copolymer (hereinafter also referred to as EVA), PP / ethylene-propylene rubber (hereinafter also referred to as EPR), PP / ethylene-butene rubber (hereinafter also referred to as EBR), Homo or block P
P / random PP, random PP / EPR, polyamide (hereinafter also referred to as PA) / LDPE, PA / HDP
E, PA / LLDPE, PA / PP, PA / EBR, P
A / EPR, polyethylene terephthalate (hereinafter PE
Also called T. ) / LDPE, PET / EPR, PET /
LLDPE etc. are mentioned. That is, as the polyolefin used for the foaming resin composition, PP, LDP
E, LLDPE, HDPE, EVA, EPR, FBR,
Examples include various ethylene-based copolymers, and those having a melting point lower than the melting point of the matrix resin by 15 ° C. or more, preferably 20 ° C. or more are preferably used. As the matrix resin, PP, LDPE, LLDPE,
HDPE, polyamide (including various copolymers), PE
T, modified polyphenylene oxide, etc., including various engineering plastics.

The foaming resin composition is generally contained in the foaming molding material (containing the matrix resin and the foaming resin composition) in an amount of 0.1 to 20% by weight, preferably 1 to 10%.
%, Particularly preferably 2 to 7% by weight. 0.
If it is less than 1% by weight, the expansion ratio is low (about 1.3 times), which is not preferable. On the other hand, if it exceeds 20% by weight, a large amount of the different resin used for the foaming resin is mixed, resulting in a large decrease in strength, which is not preferable.

In the present invention, when the foaming resin composition and the matrix resin are melt-kneaded at the time of foam molding, the foaming resin composition and the matrix resin are not completely compatible with each other. Therefore, the foaming resin composition is dispersed in the matrix resin to form an island layer (domain). To form. Further, when the temperature exceeds the decomposition temperature of the foaming agent, it is gasified inside the domain to form a foam cell. At this time, since the polyolefin having a long chain branching index of less than 0.6 around the cells has strain hardening characteristics, it is possible to stably form cells containing the gas generated by foaming. Therefore, even if the thermoplastic resin which is the matrix layer has a low viscosity, it forms a shell structure and has stable foaming moldability. Further, the foam cells are rarely united with each other, it is difficult to form continuous cells, and a good foam can be molded.

The foamed molded article of the present invention thus obtained is
Many foam cells 11 are dispersed in a matrix resin 16 made of a thermoplastic resin as shown in FIG. The foam cell 11 is formed by foaming a resin composition for foaming, and includes a diaphragm 12 and bubbles 1 surrounded by the diaphragm 12.
4 and. Further, the radius of the foam cell is 20 μm to 3.
0 mm is preferable, and 20 μm to 1.0 mm is preferable. Further, a foaming ratio of 1.1 to 5.0 can be easily obtained. On the other hand, an example of the foamed molding material of the conventional example is as shown in FIG. 3, in which the bubbles 20 are present in the matrix resin 22 made of a crosslinked thermoplastic resin. The foamed molding material 18 of this conventional example is not preferable because the matrix resin 22 is cross-linked, so the developability is low, and recycling becomes extremely difficult.

Further, as another conventional example, as shown in FIG. 4, there is one in which a large number of bubbles 30 are present in a matrix resin 32 made of a non-crosslinked thermoplastic resin. The foam 19 of this conventional example has recyclability because the matrix resin is not crosslinked, but the cells are not stable during foam molding, resulting in cell open cells, coalescence, outgassing, and the like. As a result, the foamed molded product is bad, and therefore the appearance is also poor.

On the other hand, in the foaming molding material 10 of the present invention, since the matrix resin 16 is not cross-linked, the recyclability is less problematic and the cells are stable, so that the molding property is improved.
The appearance is also excellent, and the developability does not deteriorate during shape shaping such as thermoforming and blow molding. That is, in the foam molding material of the present invention, since the melt viscosity of the foam cells is high, it is possible to reduce the coalescence of the foam cells after foaming, it is difficult to form open cells, the closed cells are kept, and the stability of the foam cells is high. Furthermore, since the foam cells can maintain closed cells, the expansion ratio can be easily controlled by adjusting the decomposition temperature of the foaming agent, the amount of the foaming agent, and the like.

[0026]

Example 1 Long chain branching index g ′ is 0.2 and melt flow rate (190 ° C .: JIS K6760) is 4.0 g /
10 minutes, to polyethylene having a density of 0.915 g / cm ³ , 10% by weight of NaHCO ₃ as a foaming agent, 4% by weight of citric acid coated with a fatty acid and 2% by weight of zinc stearate as a lubricant were mixed, and the screw diameter Is 30m
Pelletization was performed at a resin temperature of 140 ° C. using a twin-screw extruder having m and a length of 28 pitches. The pellet size was adjusted so as to have a cylindrical shape with a diameter of 3 mm and a length of 3 mm. 8% by weight of the foaming resin composition obtained above, and a melt flow rate (230 ° C .:
JIS K6758) is 2.0 g / 10 minutes and g'is 0.
92% by weight of 95 homopolypropylene was mixed. Hollow molding is a three-dimensional blow molding machine (manufactured by Takahashi Seiki Co., Ltd .;
KS2B-2M-75), and the screw used had an L / D (pitch number) of 12, a screw diameter of 50 mm, and a die diameter of 75 mm at the outermost periphery. Also, under the condition that the resin temperature at the die outlet is 170 ° C, the lip width is 2.0
A molding test was performed in mm.

The molded product having the shape shown in FIG. 2 is hollow-molded so that the diameter of the enlarged portion (diameter d ₂ ) is 80 mm and 100 m.
m, 120 mm, 140 mm, 160 mm, 180 m
These molded products were molded using respective m and 200 mm molds, and the ratio with d ₁ (all 75 mm), that is, d ₂ /
The expansion ratio was d ₁ . The results are shown in Table 1. It can be seen that it has stable foam moldability and spreadability. here,
◯ indicates that molding was possible, Δ indicates a level at which 1 to 2 molded articles can be obtained out of 10 samples, and x indicates that molding is not possible. Also, the molded product obtained in Example 1 was crushed and repelletized at a resin temperature of 200 ° C. using a vent type extruder, and then the same experiment was conducted. The results are shown in parentheses in Table 1. Although the expansion ratio is slightly low, it has the same molding processability. Therefore, it can be effectively used for products such as off products in factories.
It can be seen that it has recyclability.

Example 2 In Example 1, as the matrix resin, the melt flow rate (230 ° C .: JI
S K6758) uses 8 g / 10 min polypropylene (g '= 0.94) and the die outlet resin temperature is 16
The molding was performed in the same manner except that the temperature was 3 ° C. Table 2 shows the results.

Comparative Example 1 In Example 1, g ′ was 0.81 instead of polyethylene, and the melt flow rate (190 ° C .: JIS K6760) was 4.0 g / 10.
Molded in the same manner except that polyethylene having a density of 0.91 g / cm ³ was used. The results are shown in Table 3. d ₂ is 80
Even the mm sample is 1.6 out due to gas release and open cells.
Only double the foam was obtained.

(Comparative Example 2) A commercially available 6-fold foamed polyethylene foam molded by the chemical crosslinking method was crushed and tried with a re-pelletizing M / C for a biaxial type foam, but the degree of crosslinking was high. Could not be re-pelletized. Therefore, effective use in these factories is considered to be difficult.

Comparative Example 3 Using the foaming resin composition used in Comparative Example 1, an attempt was made to foam the matrix resin used in Example 2. The results are shown in Table 4. The expansion rate and the expansion ratio were also low, and the cell state was not favorable.

(Example 3) In Example 1, the long chain branching index g'is 0.57 and the melt flow rate (2.16k).
(gf, 230 ° C.) 1.0 g / 10 min ethylene-butene elastomer, and pelletized at a resin temperature of 130 ° C. by using ADCA (decomposition temperature 150 ° C. type) manufactured by Eiwa Kasei Co., Ltd. as a foaming agent and blending. The same test was conducted except that the amount was 5% by weight in order to make the generated gas amount the same. The results are shown in Table 5. As can be seen from Table 5, a stable foam could be obtained.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

EFFECTS OF THE INVENTION A low-foam molded article can be obtained from this foamed molding material by utilizing molding processing methods such as blow molding, sheet molding, and inflation film molding. According to the present invention, since the matrix resin in which the foam cells are dispersed is not crosslinked, it is possible to impart recyclability and improve developability. Moreover, since the polyolefin having a long chain branching index of less than 0.6, which is a diaphragm of the foamed cells, has a strain hardening property, coalescence of the foamed cells does not occur at the time of foaming, and it is difficult to form open cells. Therefore, since the foam cells are closed cells, the stability of the foam cells is high, and the expansion ratio can be easily controlled by adjusting the temperature and the amount of the foaming agent during foaming.

Further, since there is no step of crosslinking the matrix resin, it becomes possible to mold a multilayer molded product having a foam layer at once. Further, regardless of the polyolefin of the resin composition for foaming, a wide range of matrix resins can be selected, and accordingly, manufacturing conditions can be widely selected.
It is possible to manufacture a molded product having various properties depending on the purpose.

[Brief description of drawings]

FIG. 1 is a schematic view showing a foam molded article of the present invention.

FIG. 2 is a perspective view showing a hollow molded article used in a test.

FIG. 3 is a schematic diagram showing a foamed molded product using a crosslinked resin as a matrix.

FIG. 4 is a schematic view showing a foamed molded product using a non-crosslinked resin as a matrix.

[Explanation of symbols]

 11 Foam Cell 12 Membrane 14 Bubble 16 Matrix Resin 17 Foaming Ratio Measurement Position 18 Foam Molded Body Using Cross-Linked Resin for Matrix 19 Foam Molded Body Using Non-Cross-Linked Resin for Matrix 20 Bubble 22 Matrix Resin (Cross-Linked Resin) 30 Bubble 32 Matrix resin (non-crosslinked resin)

Claims (4)

[Claims] 1. 95 to 50% by weight of a polyolefin having a long chain branching index of less than 0.6 and 5 to 50% by weight of a pyrolyzable foaming agent.
And a resin composition for foaming. 2. A foam molding material comprising the foaming resin composition according to claim 1 and a thermoplastic resin having a long chain branching index of 0.6 to 1.0. 3. A foamed body having cells surrounded by partition walls in a matrix resin. 4. The matrix resin has a long chain branching index of 0.
The foam according to claim 3, which is a thermoplastic resin of 6 to 1.0, and the partition wall is a polyolefin having a long chain branching index of less than 0.6.