JPH083355A - Method for producing polypropylene-based resin foam - Google Patents

Abstract

(57) [Summary] [Structure] A camel-type polypropylene resin having a Z-average molecular weight of 1.5 × 10 ⁶ or more and having a molecular weight distribution overhanging in the polymer region is extruded and foamed, and the foamed resin strips are formed. A method for producing a polypropylene-based resin foam, which comprises bundling and fusing together. [Effect] By selecting a specific polypropyrin-based resin, the foamability is good and the cells are closed cells, and the strips of each foamed resin are firmly fused to each other, and even if there are voids, they are integrated. It becomes a foamed molded product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene used as a structural material, a cushioning material, a packaging material and the like having a large number of foamed thin strips made of polypropylene resin fused to each other and having excellent strength and cushioning properties. The present invention relates to a method for producing a resin foam.

[0002]

2. Description of the Related Art Conventionally, a foaming thermoplastic resin melt-transferred by an extruder by attaching a die having a large number of extrusion holes to an extrusion port is extruded and foamed as a plurality of strips from a large number of extrusion ports of the die. A method for producing a thermoplastic resin foam is known, in which a large number of strips are fused to each other in a softened state and bundled into a predetermined shape. However, it is difficult to stably obtain a high-quality foamed product from a polypropylene resin, which is a crystalline thermoplastic resin, by a conventional method of extruding from a large number of extrusion holes. That is, polypropylene resins are sensitive to temperature dependence of melt viscosity, and the viscosity suitable for foaming thereof is in a narrow temperature region close to the temperature at which resin crystals occur.
It is extremely difficult to perform extrusion foaming by controlling the resin temperature and the temperature of the die of the extruder in such a narrow temperature range. Furthermore, in the method of attaching a die having a large number of extrusion holes to the extrusion port and extruding, the flow of the extrusion holes partially crystallized is hindered, and uniform extrusion cannot be obtained.

[0003]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
In the 29729 publication, the die temperature is set higher than the melting point of the resin, the resin is extruded as an assembly of strips, and a frame die having a subsequent resin passage cross-sectional area is set at a temperature lower than the die temperature to form fine strips in the die. It is intended to obtain a foam by passing it through a strip assembly, foaming it, and solidifying by cooling. However, according to this method, the foam density is 0.08 g /
It is difficult to obtain a foam having a size of ³ cm ³ or less. Furthermore, the obtained foam had a low closed cell rate, and most of the cells were open cells, and thus had poor mechanical strength. The reason is that polypropylene resin, which is a crystalline resin, has a very low melt viscoelasticity above the melting point with the crystalline melting point as a boundary, so that it is difficult to hold the foamed bubbles and the cells are likely to be broken. Low bubble rate,
It is difficult to obtain a high expansion ratio.

Therefore, in order to carry out extrusion foaming of polypropylene resin like polystyrene resin, it is necessary to widen the temperature range in which polypropylene resin can be extruded and foamed, and to increase the melt viscoelasticity in the temperature range above the melting point. Therefore, attempts have been made to increase the molecular weight of polypropylene resin and to copolymerize it with other olefins. The modification of the resin by these means gave good results for the modification of the extrudability of the non-foaming sheet and the physical properties of the molded product of the non-foaming sheet, but if it was necessary to obtain the melt viscoelasticity suitable for extrusion foaming, There wasn't.

As a result of research conducted by the present inventor, the polypropylene resin suitable for extrusion foaming can be recognized by the molecular weight distribution obtained by gel permeation chromatography, and the polypropylene resin having a specific range of gel permeation chromatography molecular weight distribution is It has been found that an excellent polypropylene-based resin foam having a low viscoelasticity and a low open cell ratio and a high expansion ratio can be obtained because it has a melt viscoelasticity suitable for foaming and has less breakage of cells formed during foaming. An object of the present invention is to provide a polypropylene foam having a low open cell ratio, a high expansion ratio, excellent mechanical strength, and good cushioning properties.

[0006]

That is, the present invention provides:
A method for producing a foam by extruding a polypropylene-based resin containing a foaming agent from a die having a large number of small holes, converging the thin strips of the foamed resin while the resin is softening and fusing them to each other. In, a polypropylene resin is obtained by gel permeation chromatography,
A method for producing a polypropylene-based resin foam, characterized in that the z-average molecular weight is at least 1.5 × 10 ⁶ and the molecular weight distribution curve is a camel type having a protrusion in the polymer region, and a large number of small In the method for producing a foam, a polypropylene resin containing a foaming agent is extruded from a die having a hole, and while the resin is softening, the thin strips of the resin are converged and fused to each other, and a gel is produced. Z obtained by permeation chromatography
95-60% by weight of a camel-type polypropylene resin having an average molecular weight of at least 1.5 × 10 ⁶ and a molecular weight distribution curve with a protrusion in the polymer region.
And a method for producing a polypropylene-based resin foam, which comprises 5 to 40% by weight of a polyethylene-based resin, and the polypropylene-based resin characterized in that the voids present in the foam are 0 to 60%. It is a method for producing a foam.

The measuring method of gel permeation chromatography (hereinafter referred to as GPC) in the present invention is as follows. Measuring device: Waters, GPC 150-C type Measuring condition: Two Columns KF-80M (SHODEX: Showa Denko KK)) Column Temp. 145 ° C. Injec. Temp. 145 ° C Pump Temp. 60 ° C. Solvent used o-dichlorobenzene (1.0 ml / min) Run time 50 minutes Injec. vol. 400 μl

The information obtained by this GPC is as follows. (1) Mn number average molecular weight: This is the most basic average molecular weight obtained by measuring physical properties directly related to the number of molecules of a polymer, and depends on the total number of molecules. (2) Mw weight average molecular weight: an average molecular weight obtained when the measured physical property is directly related to the weight of the polymer, which is a root-mean-square of the molecular weight, and depends on a higher polymerization degree molecule than Mn. (3) Mz z average molecular weight: The highest average molecular weight, which is the cubic average of the molecular weights.

The polypropylene-based resin effective for obtaining the foam of the present invention is preferably a polymer having Mz of about 1.5 × 10 ⁶ or more and Mz / Mw ratio of about 3.0 or more. The polydispersity index Mw / Mn is not so important as a numerical value because it was not possible to distinguish between a polypropylene resin that gives good foamability and a polypropylene resin that shows insufficient foamability. In addition, the molecular weight distribution curve by GPC of a polypropylene resin that gives good foamability is always a shape with an overhang in the high molecular weight region. When this is illustrated, the higher molecular weight side than the peak of the molecular weight as shown by curve A in FIG. It does not show a monotonically decreasing curve, but has a curve with three or more inflection points, giving it the shape of a camel's spine. This is called a camel type in this invention. On the other hand, the molecular weight distribution curve of the polypropylene resin which gives insufficient foaming property is a simple monotonous shape which becomes a monotonically decreasing curve in the polymer region as shown by the curve B. The camel-type molecular weight distribution shows that most of the polypropylene resin is linear, but some high molecular weight components have many branches.

The camel-type polypropylene resin (A) used in the present invention is a branched polymer produced by the method described in US Pat. No. 4,916,198. Specifically, it is produced by previously treating a linear polypropylene resin with a peroxide or radiation to impart branching. The polypropylene resin may be a polypropylene homopolymer made of propylene or an ethylene / propylene copolymer resin made of a copolymer of propylene as a main component with an α-olefin as long as it satisfies the above structure. The copolymer is a random or block copolymer containing an ethylene component and is used to improve the brittleness of polypropylene.

According to the present invention, it is possible to obtain a good foam having an open cell ratio of 50% or less and an apparent density of 0.2 to 0.01 g / cm ³ and excellent mechanical strength even with a polypropylene resin foam alone. Although it is possible, by using a polyethylene resin mixed with this polypropylene resin, the brittleness is improved as compared with a polypropylene resin-only foam, and it becomes possible to impart flexibility.
Furthermore, the brittleness at low temperatures is improved. As the polyethylene resin used in the present invention, a homopolymer of ethylene, a copolymer of ethylene and α-olefin,
It is a resin selected from the copolymers of ethylene and non-olefin monomers having carbon, oxygen and hydrogen atoms in the functional groups. . As a homopolymer of ethylene, low density polyethylene (LDPE), high density polyethylene (HD
PE) and the like, and as a copolymer of ethylene and α-olefin, linear low density polyethylene (L-LDP)
E), linear ultra-low density polyethylene (VLDPE) and the like, and α-olefins include 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like. As a copolymer of ethylene and a non-olefin monomer having a carbon, oxygen or hydrogen atom in a functional group, an ethylene ionomer resin, ethylene-vinyl acetate copolymer resin, ethylene-vinyl alcohol copolymer resin, ethylene-acrylic acid Examples thereof include copolymer resins and ethylene-methyl methacrylate copolymer resins.

The mixing ratio of the polypropylene resin and the polyethylene resin is preferably 95 to 60% by weight of the polypropylene resin and 5 to 40% by weight of the polyethylene resin, and the ratio of the polyethylene resin to the polypropylene resin is 5% by weight. When the amount is less than 40%, the effect of imparting flexibility to the polypropylene resin foam is small, and when the amount of the polyethylene resin exceeds 40% by weight, the foamability is lowered, and the open cell ratio increases and the expansion ratio decreases. Therefore, it becomes difficult to obtain a good foam.

Other than the selection of the resin in the present invention, a foaming agent, a cell regulator, a crystal nucleating agent, a flame retardant, a deterioration inhibitor, a pigment, an antistatic agent, and a shrinkage inhibitor which are used in ordinary extrusion foaming are appropriately used. Is added.

For example, as the foaming agent, a heat-decomposable solid compound, a volatile liquid, a gas, an inert gas or the like can be broadly divided and used alone or in a mixture. Specifically, as the thermal decomposition type solid compound, azodicarbonamide, dinitrosopentamethylenetetramine, etc. can be used, and as the volatile liquid or gas, propane, normal-butane, iso-butane,
Saturated aliphatic hydrocarbons such as normal-pentane, iso-pentane and neo-pentane, saturated alicyclic hydrocarbons such as cyclopentane and cyclohexane, halogenated carbonization such as trichlorofluoromethane and dichlorotetrafluoroethane Hydrogen, ethers such as dimethyl ether, ketones such as acetone, methanol,
Alcohols such as ethanol, water and the like can be used. Further, carbon dioxide, nitrogen or the like can be used as the inert gas.

As the bubble control agent, fine powder talc, silica, or a mixture of sodium hydrogen carbonate and citric acid can be added. In addition, pigments, antistatic agents, flame retardants, antioxidants, etc. can be mixed. In addition, as the extruder, a tandem extruder of a type in which two extruders are connected in series is often used. Also in this invention, the tandem extruder is used to supply the resin to the first extruder, It is preferable that a foaming agent be pressed into the foamed product from the tip to form a foamable melt, which is then cooled to a foaming suitable temperature in an extruder and then extruded from a porous die.

The foam molded by being extruded from a die provided with a large number of extrusion holes provided in an extrusion port may have voids formed in the foam depending on the hole shape of the die and the space between the holes.
The void means not a bubble constituting a foam but a space existing between a large number of extruded and foamed strips. The formation of voids depends on the distance between holes, the diameter of the holes, the position,
Since the diameter and interval of each foamed strip can be changed by changing the number of foams, it is possible to arbitrarily control the position, ratio, shape, etc. of the voids in the foam. According to the invention, the shape of the holes may be round, square, polygonal, slit or any other shape. Further, if the arrangement of the strips extruded and foamed from the porous die is parallel to the extrusion flow direction, the voids generated between the strips will be straight and parallel to the longitudinal direction of the foam. If the thin strips are folded by the method described in Japanese Patent Publication No. 58-9745, the voids can be generated at regular intervals or can be generated at unequal intervals.

Further, for example, the volatile type foaming agent used in the production of the foam is preferably replaced quickly with air from the foam, but as the thickness of the foam increases and the volume as a whole increases, the replacement is performed. The period of being played becomes longer. Since the foam produced according to the present invention has voids, it is possible to quickly replace the foaming agent with air from the voids exposed to the atmosphere even if the volume of the foam increases, and the replacement is required. It is possible to reduce the period considerably.

The foam obtained by the present invention preferably has a porosity of 0 to 60% and an open cell ratio of 5
A foam having an apparent density of 0.2 to 0.01 g / cc of 0% or less has excellent strength and cushioning properties, and is effective as a structural material, cushioning material, packaging material and the like.

[0019]

Embodiments will be described in detail below with reference to embodiments. The test evaluation was performed by the following methods. 1. Compressive strength The foam was cut into a size of 25 mm in thickness and 50 mm in width and length to obtain a measurement sample. This measurement sample is JIS-K6
According to 767, the strength of the foam in the extrusion flow direction and the thickness direction is measured when the strength is compressed to 25% of the measurement sample. 2. Bending test 25mm thick foam, 50mm width, 150mm length
The sample was cut into a size of 3 to obtain a measurement sample. The bending strength in the extrusion flow direction and width direction of the foam was measured for this measurement sample according to JIS-K6767 with a span interval of 100 mm. 3. Elastic modulus It is obtained as a compressive elastic modulus and a flexural elastic modulus by performing measurement by the same method as the measuring method of the compressive strength and the bending test. Elastic modulus is the compressive stress experienced by a material within the elastic limit of the test material,
It is the value obtained by dividing the bending stress by the strain generated in the material. The smaller this value, the greater the deformation under a constant load, the softer the contact, the greater the flexibility, and the greater the recovery elasticity.

4. Open cell ratio The obtained foam was cut into 25 mm in thickness, width, and length to obtain a measurement sample. This measurement sample is designated ASTM D-28.
By the air displacement method according to 56, the volume ratio of the interconnected bubbles in the measurement sample was obtained, and the open cell ratio was calculated.
The true volume of the sample (volume of the resin portion only) was determined by immersing the measurement sample in a graduated cylinder filled with water and by raising the height of the water surface. Therefore, this open cell does not include voids existing between the strands, and means the open cell rate occupying the true volume of each individual strand. 5. Porosity The obtained foam is 20 mm in thickness, 50 mm in width, and 10 in length.
The sample was cut into 0 mm and used as a measurement sample. The porosity of this was determined according to the following formula. Porosity = (A−B) / A × 100 A: Apparent volume including voids of sample B: True volume of only resin portion not including voids of sample (determined from 4.)

In each of the examples and comparative examples, the polypropylene resin used has the physical property values shown in Table 1.

[Table 1]

In Examples 3 to 11, the formulations shown in Table 2 were used.

[Table 2]

The foams produced according to the respective examples have the physical properties shown in Table 3.

[Table 3]

[0024]

【Example】

Example 1 Camel type polypropylene resin A (PP homopolymer,
Hydrocerol HK (manufactured by Boehringer Ingelheim), which is a mixture of citric acid and sodium bicarbonate as a foam control agent, is added to 100 parts by weight of Himont Co., Ltd.
Part by weight is mixed in advance with a blender, and the mixture is supplied to a tandem extruder in which two units having a diameter of 50 mm and a diameter of 65 mm are connected. The mixture supplied to the first extruder adjusted to 150 to 230 ° C. was melt-kneaded, and butane as a foaming agent was added to the base resin from the tip of the extruder to 8.0.
It was pressed in at a ratio of parts by weight. 180-145 degrees Celsius that continues thereafter
The mixture was introduced into the second extruder adjusted to 1, and the resin temperature was adjusted to a temperature suitable for foaming (about 158 ° C),
It was extruded from a die kept at 58 ° C. As the die, there is used a die in which holes having a diameter of 1.2 mm are opened laterally at intervals of 4.5 mm in 33 rows in 13 rows on the extrusion surface of the die. Further, since the holes are arranged so as to be offset for each row with a half interval therebetween, when the three holes are seen, the respective holes are arranged at the positions of the vertices of the equilateral triangle. The resin extruded from each of the extrusion holes of the die progresses into a large number of foamed strips S, which are foamed and fused to each other in the meantime to have a thickness of 50 mm, a width of 152 mm, and a density of 152 mm as shown in FIG. 0.05
At 78 g / cm ³ , a foamed molded product having voids (porosity 3.8%) penetrating in parallel between the strips S was obtained. The properties of the resulting foam are shown in Table 3.

Example 2 100 parts by weight of a camel-type polypropylene resin B (PP-PE random copolymer, manufactured by Highmont Co.) having an Mz of 202.4 × 10 4 was added to Hydro, which was a mixture of citric acid and sodium bicarbonate as a cell regulator. 0.2 parts by weight of Celol HK (Boehringer Ingelheim) was mixed in advance with a blender, and the mixture was calibrated with a diameter of 50 mm.
And 65 mm are fed to an extruder in which two units are connected. 150
The mixture supplied to the first extruder adjusted to ˜230 ° C. was melt-kneaded, and butane as a foaming agent was pressed into the base resin at a ratio of 8.0 parts by weight from the tip of the extruder. The mixture is then introduced into a second extruder, which is subsequently regulated at 180 to 145 ° C., at a temperature suitable for foaming (15
The resin temperature was adjusted to 8 ° C.) and the resin was extruded from a die kept at 158 ° C. As a die, a diameter of 1.
33 2 mm holes horizontally with a 4.5 mm spacing, 1
Use the one opened in one row. Of these, four holes are arranged at the positions forming the vertices of a square. The resin extruded from each extrusion hole of the die progresses into a large number of strips S, which are foamed and fused to each other to be united as shown in FIG. 047
At 5 g / cm ³ , a foamed molded product having voids (porosity 13.6%) penetrating in parallel between the strips S was obtained. The properties of the resulting foam are shown in Table 3.

In Examples 3 to 11, as shown in Table 2, a polypropylene resin composed of the polypropylene resin A of Example 1 and various polyethylene resins was used. Example 3 Camel type polypropylene resin A (PP homopolymer,
85 parts by weight of Himont Co., Ltd. and Hi-Zex 5305E (manufactured by Mitsui Petrochemical) 15 which is a high density polyethylene resin.
0.2 parts by weight of hydrocerol HK, which is a mixture of citric acid and sodium bicarbonate as a bubble control agent, was previously mixed in a blender with a blender, and the mixture was extruded in the same manner as in Example 1. The properties of the foam obtained are shown in Table 3.
As shown in (1), the elastic modulus is lowered and the flexibility is increased.

Examples 4 to 11 Extrusion was carried out in the same manner as in Example 3 with the compounding ratios shown in Table 2. The properties of the resulting foam are those with increased flexibility as shown in Table 3.

Example 12 Extrusion was performed in the same manner as in Example 1 except that the porous die was changed to the die M shown in FIG. As the base M, on the extrusion surface of the base M,
The holes H with a diameter of 1.4 mm are set to 1 horizontally with an interval of 10 mm.
The holes H were opened in 0 holes and 5 rows, and the holes H were 9 holes in which holes 1.8 having a diameter of 1.8 mm were laterally opened in 4 rows. The foam extruded from the base M is
When the take-up speed is adjusted to the strip having the small hole, the strip S having the larger diameter of the hole H has a larger resin flow rate, and therefore, FIG.
The strips S are extruded as described above to form a folded foamed body having a large void inside. As shown in Table 3, the obtained foam has a large void ratio of 48% and a small apparent density.

COMPARATIVE EXAMPLE 1 Camel type in GPC, Mz <1.5 × 10
Polypropylene resin C of ^-6 was extruded in the same manner as in Example 1. The density of the obtained foam = 0.0733 g
/ Cm ³ , but the open cell ratio was as large as 64%, and the strength was weakened, and no good foam was obtained.

Comparative Examples 2 and 3 Polypropylene resins D and C shown in Table 1 which had a simple chevron shape in GPC were extruded in the same manner as in Example 1, but the resulting foams had a density of 0.3 g / cm ³ or more. It is difficult to say that a good foam is used, and when the temperature of the resin is lowered near the foaming suitable resin temperature, part of the resin begins to crystallize, causing a part of the hole in the gold port to be clogged. It became difficult to extrude uniformly.

Comparative Examples 4 to 6 Attempts were made in the same manner with the compounding ratios shown in Table 2. However, uneven dispersion of the resin was observed and the foam immediately contracted immediately after extrusion, so that the expansion ratio was low and good. No foam was obtained.

[0032]

Industrial Applicability The present invention is constructed as described above and has a z-average molecular weight of at least 1.5 × 10 ⁶ obtained by gel permeation chromatography and a molecular weight distribution curve in which the curve extends to the polymer region. Since a camel-type polypropylene resin of a certain shape is used, each foamed resin strip has good foamability, has many closed cells, and has a high expansion ratio, and must be a foam with excellent compression and bending strength. Can be done. Further, according to the present invention, since the polypropylene resin has good foamability and is a closed cell, the strips of each foamed resin are firmly fused to each other, and a foam body in which the strips are converged and integrated can be manufactured. Further, in the present invention, since the foamed resin strips are firmly fused to each other, the foamed strips should retain the shape of the integrated foam even with partial fusion with voids. You can The voids can have a porosity of 60%, which can reduce the apparent density of the foam. Further, in the present invention, by mixing the polypropylene resin with the polyethylene resin, it is possible to give the foam with flexibility, which is excellent in cushioning property.

[0033]

[Brief description of drawings]

FIG. 1 is a graph showing a molecular weight distribution curve.

FIG. 2 is a perspective view of a foam obtained according to the present invention.

FIG. 3 is a perspective view of another foam obtained according to the present invention.

FIG. 4 is a front view showing an example of a porous die used in the present invention.

FIG. 5 is a cutaway sectional view of an extruder showing an embodiment of the present invention.

[Explanation of symbols]

 S Fine line of foamed resin E Void M Base H

Claims (3)

[Claims] 1. A foaming agent is contained in a die having a large number of small holes.
Extruded the polypropylene resin that had, the resin softened
Foamed resin strips are focused and fused together during
In the method for producing a foam,
The resin can be analyzed by gel permeation chromatography.
And a z-average molecular weight of at least 1.5 × 10
⁶And the molecular weight distribution curve is
Characterized by a camel type with overhang
A method for producing a polypropylene-based resin foam. 2. A z-average molecular weight of at least 1.5 ×, obtained by gel permeation chromatography.
95% to 60% by weight of a polypropylene resin having a molecular weight distribution curve of 10 ⁶ and having a curve protrusion in the polymer region and a polyethylene resin 5
The method for producing a polypropylene-based resin foam according to claim 1, wherein the polypropylene-based resin foam comprises 40 to 40% by weight. 3. The method for producing a polypropylene resin foam according to claim 1 or 2, wherein the voids present in the foam are 0 to 60%.