JPH0925354A - Bundle of extrusion-foamed polypropylene resin strings and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a bundle of extrusion-foamed polypropylene resin strings which is excellent in cushioning properties, hardly undergoes the degradation in cushioning properties even after a repeated falling down test, and does not allow the separation of strings by using a foamable compsn. contg. a PP resin having special viscoelastic characteristics. SOLUTION: This bundle of extrusion-foamed strings is produced by kneading a foamable compsn. comprising a PP resin and a volatile blowing agent contained therein at a high temp. and pressure, extruding the compsn. through a multiperforated die into a low-temp. low-pressure zone to form the compsn. into foamed strings, and introducing the strings into a forming apparatus to fuse them to each other to integrally bundle them, subject to the condition that the PP resin exhibits a biaxial-elongation viscosity of 4.5×10<6> P at a biaxial- elongation strain of 0.2 and a biaxial strain hardening ratio of 0.30 or higher. Thus obtd. bundle has a density of 0.005-0.04g/cm<3> , a wall thickness of 20mm or higher, an average closed cell size of 0.4-2.0mm, and a closed cell content of 80% or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene resin extruded foamed strip bundle and a method for producing the same. The extruded foamed strip bundle is cut into various shapes to form a cushioning packaging material, a floating material, and a heat insulating material. Used in fields such as.

[0002]

2. Description of the Related Art A foaming composition containing a polypropylene resin and a volatile foaming agent is kneaded at high temperature and high pressure, and then adjusted in temperature to form a strip from an extrusion die having a plurality of extrusion holes under low temperature and low pressure. A method for producing a polypropylene-based resin extruded foamed strip bundle in which a plurality of foamed strips are fused and integrated by introducing and converging the foamed strips into a molding device is known ( See, for example, JP-A-53-1262). In this publication, by using a narrow extrusion hole of a die having a protrusion on the resin entrance side, the retention of the crystalline thermoplastic resin at a temperature near the foaming temperature is prevented, and the foamability is hindered by the outflow of the crystallized resin. Suggests ways to prevent it. In the publication, MH-8 manufactured by Mitsubishi Petrochemical Co., Ltd. is used as a polypropylene resin in the examples, and the thickness is 14 mm and the width is 1 mm.
A polypropylene resin extruded foamed strip bundle having a density of 0.15 g / cm ³ at 50 mm is obtained.

As an extrusion foaming resin, it is proposed in JP-A-4-363227 to use a propylene resin having a melt tension of 7 gf or more at 230 ° C. On the other hand, the polypropylene-based resin extruded foam fine strip bundle of the present invention is mainly used for home appliances such as audio having a weight of about 5 to 50 kg, OA equipment such as personal computers, and also for cushioning precision equipment having a similar weight. It is used as a packaging material and requires the following characteristics.

That is, FIG. 3 shows a polyethylene resin extruded foam (having a density of 0.025 g / cm ³ and a wall thickness of 20, 30, 40 mm, respectively, according to JIS Z0235 “Dynamic compression test method for cushioning material for packaging”). 3] is a graph of a dynamic impact characteristic curve showing the relationship between the thickness of the foam and the maximum acceleration when the foam is dropped once. FIG. 3 shows the meaning of the “buffering performance” of the extruded strip-shaped foam according to the present invention, and an extruded foamed strip bundle having a wall thickness of 20 mm or more is required to effectively develop this “buffering performance”. It indicates that there is.

In the graph showing the dynamic impact characteristic curve of FIG. 3, the vertical axis represents the maximum acceleration J (0 to 100 G) and the horizontal axis represents the static stress I (0.02 kgf / log scale).
cm ^{2 to} 0.4 kgf / cm ² ). This graph is 6
Drop the weight with built-in accelerometer from the height of 0 cm,
The maximum acceleration measured by the accelerometer when dropped is the maximum acceleration, and the stress generated in the foam when the weight is left stationary on the foam is the static stress, and the relationship between the two is plotted. The static stress in this case is 5 to 5
0.02 kg when about 0 kg of home electric appliances such as audio equipment, OA equipment such as personal computers, and precision equipment of the same weight are left standing on the foam.
was kgf / cm ² or more 0.4kgf / cm ² or less.

The symbols t20, t30, and t40 in FIG. 3 indicate the thickness of the foam body (mm). The lowest maximum acceleration in the above static stress range (hereinafter referred to as the "minimum value of maximum acceleration") is the smallest when the foam is used as a cushioning packaging material for home appliances, etc. It indicates the maximum acceleration (load), that is, the highest "buffer performance" value of the foam.

Generally, it is said that the maximum acceleration at which the above-mentioned home electric appliances or the like do not break down or be damaged is 80 G or less. Therefore, the wall thickness is 20 mm in the static stress range.
For foams of less than 80%, the maximum acceleration applied to products such as the above-mentioned home electric appliances which are the objects to be packaged when the package falls down is 80.
Since it exceeds G, there is a high possibility that the product will break down or be damaged, and it means that a foam having a wall thickness of less than 20 mm is difficult to use as a cushioning packaging material for the above home electric appliances and the like.

[0008]

However, when the resin used in the above-mentioned publication is used, the density of the resin is 0.
An attempt was made to produce a polypropylene resin extruded foamed strip bundle of 04 g / cm ³ and a wall thickness of 20 mm, but the obtained extruded foamed strip bundle had a closed cell ratio of less than 30% and a buffer against repeated drops. There is a problem such as a significant decrease in performance, and even if measures are taken to increase the closed cell rate, the closed cell rate does not rise sufficiently and the bubble diameter is 0.4 mm. In addition to the fact that the compression stress of the bundle is greatly anisotropy, and the surface appearance of the foamed strips has scale-like irregularities and the surface appearance is poor, the fusion force between the foamed strips is significantly reduced. It causes a problem such as a decrease in

That is, in the resin used in the above publication, the density is 0.04 g / cm ³ or less and the wall thickness is 2
A polypropylene-based resin extruded foam fine strip bundle having a size of 0 mm or more cannot be obtained. The object of the present invention is to have a density of 0.005 g /
A polypropylene-based resin extruded foamed fine strip bundle having a thickness of 20 mm or more and a cm ³ or more and 0.04 g / cm ³ or less,
The average cell diameter is 0.4 mm or more and 2.0 mm or less, the closed cell rate is 80% or more, the anisotropy of the compression stress is small, the surface of the bundle has no irregularities, and the extruded foamed strips have excellent fusion bonding properties. Therefore, it is an object of the present invention to provide a polypropylene-based resin extruded foamed fine fiber bundle which maintains good cushioning performance, has small anisotropy in cushioning performance, and is easy to design, and a method for producing the same.

[0010]

Means for Solving the Problems The composition of the extruded foamed strip bundle of the present invention has a biaxial elongation strain of polypropylene resin of 0.
The biaxial extensional viscosity in 2 is 3 × 10 ⁶ poise or more,
The biaxial strain hardening rate α is 0.25 or more [however, the biaxial strain hardening rate is expressed by the following equation: α = 0.77 × (log η ₂ −log η ₁ ), where η ₁ is the biaxial elongation strain 0. Is 0, and η ₂ represents the biaxial extensional viscosity when the biaxial extensional strain is 0.2.)], And the density of the extruded foamed strip bundle is 0. .005g / cm ³ or more 0.04 g / cm ³ or less, an average cell diameter 0.4mm or 2.0mm or less, closed cell ratio of 80% or more, polypropylene resin thickness is equal to or is 20mm or more It is an extruded foam strip bundle.

Further, the construction of the method for producing an extruded foamed fine fiber bundle of the present invention is such that a foamable composition comprising a polypropylene resin and a volatile foaming agent is kneaded under high temperature and high pressure and then adjusted in temperature to obtain a plurality of components. The above-mentioned extrusion in which a strip is extruded from a die for extrusion having an extrusion hole to a region under low temperature and low pressure to foam, and the strip is introduced and focused into a molding apparatus and a plurality of strips are fused and integrated with each other. In the method for producing a foamed thin fiber bundle, the biaxial elongation viscosity at a biaxial elongation strain of 0.2 of the polypropylene resin is 4.5 × 10 ⁶ poise or more, and the biaxial strain hardening rate α is 0. .30 or more [however, the biaxial strain hardening rate is expressed by the following equation: α = 0.77 × (log η ₂ −log η ₁ ), where η ₁ is the biaxial extensional viscosity when the biaxial extensional strain is 0.01. , And η ₂ is defined as the biaxial extensional viscosity when the biaxial extensional strain is 0.2). A method for producing a polypropylene-based resin extruded foamed strip bundle, which comprises using a pyrene-based resin.

The contents of the present invention will be described in more detail below, but the manufacturing method will be described in detail for convenience of explanation. The manufacturing method of the present invention differs from the prior art in that a polypropylene resin having special viscoelastic properties (“biaxial elongational viscosity” and “biaxial strain hardening rate α”) is used. First, the difference from the prior art in terms of the extrusion foaming method will be described.

The origin of the extrusion foaming method is to suppress "foaming in extrusion die". FIG. 1 is an explanatory view showing a process of forming an extruded foam strip bundle and a bubble growth process in the vicinity of an extrusion die of an extruder, and is a conceptual diagram showing the bubble growth process inside and outside the system. In FIG. 1, A in the arrow indicates a land area of the extrusion die, B indicates a taper area of the extrusion die, and C indicates a tip area of the extruder. The direction of the arrow indicates the height of the flow pressure, and the height relationship of the measured values of the flow pressure in each region at the extrusion rate Q1 of the foamable composition capable of obtaining a high foam of 0.04 g / cm ³ or less is shown. It is a figure. A line 4 (one-dot chain line) that traverses the line graph in FIG. 1 indicates the vapor pressure at the system temperature of the used blowing agent. Furthermore, D of FIG.
Shows a process for forming an extruded foamed strip bundle in the case of a foamable composition using the resin 3 used for producing the extruded foamed strip bundle foam of the present invention. Mark E
1 and E2 show the generation of bubbles in the foamable composition and the growth process thereof. Also, line 1 in the line graph above
Is a resin 3 (MFR: 1.9, biaxial extensional viscosity: 6.7 × 1) used in the production of the extruded foamed strip bundle of the present invention.
0 ⁶ is the flow pressure value in the case of biaxial strain hardening rate α: 0.48), and the polygonal lines 2 and 3 are conventional extruded foamed strip bundles shown for comparison and the fusion pressure shown in the publication. It is a flow pressure value of a resin (commercially available product) used in the production of a single extruded foam having no adhered surface (hereinafter referred to as Planck foam). That is, the polygonal line 2 is the resin 12 (commercially available resin; MFR: 0.5, biaxial extensional viscosity: 4.2 × 10 ⁶ , biaxial strain hardening rate α) used for manufacturing the extruded foamed strip bundle of the comparative example. : 0.22), and the polygonal line 3 is resin 14 (commercially available resin; MFR: 3.0, biaxial extension viscosity: 2.5 × 10 ⁶ , 2) which is also used in the production of the extruded foamed strip bundle of the comparative example. Axial strain hardening rate α: 0.44)
Is the value for

In FIG. 1, first, the resin (polygonal line 1) used in the production of the extruded foamed strip bundle of the present invention is used in the production of conventional extruded foamed strip bundles and plank foams. The pressure inside the system is generally higher than that of the existing resin (polygonal lines 2 and 3), and the high flow rate is well above the vapor pressure line 4 at least in the upstream region of the land area (A) of the extrusion die. It can be seen that this indicates pressure. Generally, the intersection of the vapor pressure line 4 and the polygonal line (flow pressure value) is the starting point of bubble formation. Therefore, in the resin (polygonal line 1) used for producing the extruded foamed strip bundle of the present invention, foaming is completely suppressed on the upstream side of the area (A), and the bubbles E1 are generated for the first time in the area (A). The bubbles E1 gradually grow into large bubbles E2 while being pushed out of the die.
In other words, it can be seen that the resin used for producing the extruded foamed strip bundle of the present invention is a resin having a flow viscosity characteristic sufficient to suppress "foaming in extrusion die".

On the other hand, the resins (the polygonal lines 2 and 3) used in the production of the conventional extruded foam strip bundle and plank foam have flow viscosity characteristics capable of suppressing "foaming in the extrusion die". Clearly not. Therefore, as a phenomenon (the generation of bubbles is not shown), foaming occurs in the region (B), the linear velocity of the extruded foam strip in the extrusion direction after the region (B) is increased, and As a result of a sudden drop in pressure, a large number of minute bubbles are generated instantaneously, and at the same time the extruded foam strips are rapidly cooled by the latent heat of the foaming agent during foaming, and the solidification of the extruded foam strip outer peripheral surface progresses in the system. Since the extruded foam strips are extruded in this state, the diameter of the extruded foam strips is close to the diameter of the die opening, and the thickness of the extruded foam strips formed by bundling the extruded strips can only be reduced. In the extrusion at this time, the surface appearance of each extruded foam strip is poor due to friction at the land of the extrusion die, and the surface appearance is poor. Since they do not come into contact with each other, the extruded foam strips have a very low fusion force, and the extruded foam strips are separated from each other after repeated dropping or during cutting, which poses a serious problem in practical use. As a result, the resin (polygonal lines 2 and 3) used in the production of conventional extruded foam strip bundles and plank foams
Then, a normal extruded foam strip bundle cannot be obtained.

The above-mentioned difference in the flow viscosity characteristics is a matter which cannot be discussed in the conventional relations such as the magnitude relation of the MFR and the magnitude relation of the melt tension value, and the study by the present inventors, that is, the system at the time of extrusion. Since the increase of the flow pressure value in the inside should be governed by the extensional flow of the resin when flowing in the taper portion region B of the extrusion die, it is necessary to take the extensional viscosity into consideration. This difference was finally clarified by a study focusing on "," and the extruded foam fine-fiber bundle composed of this resin could be successfully realized.

That is, "the biaxial extensional viscosity at a biaxial extensional strain of 0.2 is not less than 4.5 × 10 ⁶ poise" in the resin used for producing the extruded foamed strip bundle of the present invention (extrusion foaming). In the resin that makes up the strip bundle, "biaxial extension strain 0.2
Has a biaxial extensional viscosity of 3 × 10 ⁶ poise or more. ”)
First of all, the necessity of the requirement is that the suppression of "foaming in extrusion die" which is the origin of the extrusion foaming method can be easily achieved by the characteristics of the resin. Therefore, the resin used in the production of the extruded foam fine-strip bundle of the present invention suppresses "foaming in extrusion die" even when an extrusion foaming apparatus such as a conventional polyethylene-based resin is used, and has a thick and high quality. A substrate for manufacturing extruded foam strip bundles can be easily created. According to experiments conducted by the present inventors, the "biaxial extensional viscosity" of the resin used for producing the extruded foamed thin fiber bundle is 15 × 10 ⁶ poi.
We have succeeded in producing a resin that becomes an SE, and can easily produce extruded foam strip bundles with large cross-sections having various cross-sectional shapes (shapes of the surface perpendicular to the extrusion direction) with extruders of various performances. From the viewpoint of wanting to obtain, the "biaxial extensional viscosity" of the resin used for producing the extruded foamed strip bundle is 6.0 to 15.0.
It is desirable to select a resin in the range of (× 10 ⁶ poise).

Next, the role of the "retention of cells having a large diameter and having a large number of closed cells", which is the most important in the extrusion foaming having a special viscoelastic property, will be described. FIG. 2 is an explanatory diagram, and is a conceptual diagram showing the formation of extruded foamed strip bundles and the growth process of bubbles in the vicinity of the extrusion die of the extruder when the resin flow pressure of the polygonal line 3 in FIG. 1 is mechanically increased. Is. Therefore, the point different from FIG. 1 is to increase the extrusion rate to Q2 of the foamable composition using the polygonal line 3 (a commercially available resin used in the production of conventional plank foam) to increase the shear rate. The measured value of the flow pressure at
(3 ") shows a process for forming an extruded foamed strip bundle in the vicinity of an extrusion die of an extruder in a conceptual diagram of a bubble growth process. 3'is the same composition component as that of 3 in FIG. In the case of (3), the growth process of bubbles (extruded foamed strip bundles) outside the system is indicated by the broken line F ', and 3 "is the case of the above 3'composition component for improving the bubble retention. The growth process of air bubbles (extruded foam strip bundles) outside the system is indicated by a solid line F ″.

In FIG. 2, the flow pressure of the foamable composition can be adjusted by the relative shear rate of the foamable composition in the system (relationship of extrusion rate to die opening size), and as a result It has been shown that the suppression of "foaming in the extrusion die" is possible by selecting the extrusion device. This adjustment is apparently unlimited, ignoring the economics of the equipment. Therefore, in the case of the polygonal lines 3 ′ and 3 ″ in FIG.
As in the case of the polygonal line 1, the foaming is completely suppressed on the upstream side of the area (A), and the bubbles G1 are not formed in the area (A) for the first time.
Occurs, and the bubble G1 is extruded out of the die and adjusted to grow into G2. Therefore, in particular, in the case of the polygonal line 3'shown in FIG. 2, in the state of the process of forming the thickness of the extruded foamed strip bundle after extrusion, as shown by the broken line F ', the expansion starts as compared with D in FIG. Although the position of the extruded foamed strip bundle becomes thinner as the position recedes, there is no apparent difference outside that. However, the problem in this case (the detailed description is omitted because it is difficult to illustrate) is that the formed extruded foam strip bundle is formed inside the extruded foam strip bundle during the process of cooling and solidification. The air bubbles that were supposed to have been severely broken,
That is, the closed-cell rate drops sharply. The phenomenon of bubbles communicating due to this foam breaking creates a state in which a cavity like a nest (hereinafter referred to as a void phenomenon) is created inside the extruded foamed strip bundle as the thickness of the extruded foam strip bundle is increased. However, there is a fatal problem that an extruded foamed strip bundle having a thickness of 20 mm or more cannot be obtained with a high closed cell rate.

As a measure against this, for example, if an attempt is made to increase the closed cell ratio by increasing the amount of the bubble nucleating agent to make the composition of the component 3 ", the bubble G1 is first formed in the region (A) as in the case of the polygonal line 3 '. This bubble G1 is pushed out of the die and tries to grow into G2, but the problem in this case is that
In the area (A), a large number of minute bubbles G1 are instantly generated. Due to the rapid cooling of the foaming agent latent heat during the foaming of a large number of bubbles generated at that instant, the outer peripheral dimension of the extruded foamed strip is rapidly solidified and the outer peripheral dimension is determined before the growth of the bubbles is completed. Since the diameter is larger than in other directions, the cross-sectional area of the extruded foam strips and the thickness of the extruded foam strip bundles that condense them do not increase, and the compressive stress in the extrusion direction is significantly higher than in the thickness direction. Therefore, the cushioning performance changes greatly depending on the direction of use of the extruded foam strips, and the cushioning design is very difficult.Furthermore, due to the rapid solidification of the extruded foam strips, the fusion of the extruded foam strip surfaces is poor. In addition, the diameter of the extruded foam strip becomes small, and the contact pressure between the adjacent extruded foam strips does not occur or decreases remarkably immediately after foaming, resulting in a drastic decrease in the fusion force between the extruded foam strips. . In such an extruded foam strip bundle, separation occurs between the extruded foam strips during the above-mentioned repeated dropping or cutting, which poses a serious problem in practical use.

In other words, when a high foam is used, the resin (commercially available product) used for the conventional extruded foam strip bundle and plank foam is "a bubble communication phenomenon due to bubble breakage" and "a small diameter bubble". There is room for conditional improvement to avoid both defective phenomena such as the phenomenon that the anisotropy of compressive stress becomes strong without increasing the thickness of the foam and the fusion force between the extruded foam strips decreases. In the end, the process of forming the extruded foamed strip bundle as shown in FIG. 1 (resin used in the production of the extruded foamed strip bundle of the present invention), that is, an appropriate number of minute particles generated in the region A The bubbles E1 are gently extruded out of the system, and large bubbles E2
It is impossible to form a foaming process that grows to form an expansion locus D and is cooled and fixed as substantially spherical bubbles rich in closed cells to form a high-quality thick extruded foam strip bundle.

The difference between the resin used in the production of the extruded foamed strip bundle of the present invention and the resin (commercially available product) used in the conventional production of the extruded foamed strip bundle and the plank foam. Is an essential property of a resin, that is, a resin used in the extruded foamed thin fiber bundle of the present invention that has “rich large closed cell properties and cell retention”, and a conventional resin that does not have this property. This is a difference from the resin (commercially available product) used in the production of the extruded foam strip bundle and the plank foam.
That is, the resin used in the production of the extruded foam strip bundle of the present invention has the above-mentioned "biaxial extensional viscosity at a biaxial extensional strain of 0.2 or more of 4.5 × 10 ⁶ poise" (extrusion foaming). In addition to the requirement that "the biaxial extensional viscosity at a biaxial extensional strain of 0.2 is 3 × 10 ⁶ poise or more at a biaxial extensional strain of 0.2 or more"), the resin constituting the strip bundle has a "biaxial strain hardening rate α of 0.30. Or more "(" biaxial strain hardening rate α is 0.25 or more "in the resin forming the extruded foamed strip bundle) is the difference.

The inventors of the present invention have studied the phenomenon of the above-mentioned bubble breakage and the communication of bubbles in the cooling and solidification process of the extruded foamed thin fiber bundle, and as a result, this phenomenon is caused by the "bubble film cooling of the resin itself forming the bubble film. It was inferred that it was based on two drawbacks: "easiness of tearing of bubble film during solidification process" and "difficulty of forming bubble film of uniform thickness during bubble growth process". Furthermore, the "biaxial extensional viscosity" is based on the hypothesis that the characteristics of at least the biaxial direction should be considered because the bubble film forms the surface.
Finally, by paying attention to “biaxial strain hardening rate α”, the resin used in the extruded foamed strip bundle of the present invention was finally completed, and as a result, the extruded foamed strip bundle targeted by the present invention was obtained. It was successful in being completed. Also, of course,
The properties noted for the resin that make up the extruded foam strip bundle are those resulting from the properties of the resin used to make the extruded foam strip bundle.

That is, "the biaxial extensional viscosity at a biaxial extensional strain of 0.2 is not less than 4.5 × 10 ⁶ poise at the biaxial extensional strain of the resin used for producing the extruded foamed article bundle (extruded foamed article bundle). For the resin that constitutes the body, the role of the requirement that "the biaxial extensional viscosity at a biaxial extensional strain of 0.2 is 3.0 x 10 ⁶ poise or more") is that of the cell membrane resin that is still in a fluid state. It is to suppress the fluidity to make the bubble film tough, and to prevent the formed bubble film from rupturing against the surface tension during the process of cooling and solidification. On the other hand, "the biaxial strain hardening rate α is 0.30 or more" of the resin used for manufacturing the extruded foamed strip bundle (for the resin constituting the extruded foamed strip bundle, the "biaxial strain hardening rate α is The role of the requirement of "0.25 or more") is to form a bubble film having a uniform thickness by uniformly flowing the bubble film resin that is still in a flowable state, and the bubble film becomes thin and thin during extension. Also in this case, the extension of the thick portion is preferentially promoted to suppress the formation of the thinned film as a whole,
The purpose is to prevent breakage of the bubble film from the thin film portion in the process until the cooling and solidification of the bubble is completed. Therefore, from the above viewpoint, when it is desired to obtain a high-quality extruded foam strip bundle having a higher closed cell rate, the "biaxial extensional viscosity" of the resin used for producing the extruded foam strip bundle is 5.0. × 10 ⁶ poi
se or more (for the resin forming the extruded foamed strip bundle, 3.
3 × 10 ⁶ poise or more), and the “biaxial strain hardening rate α” is 0.35 or more (0.30 or more in the resin constituting the extruded foamed thin fiber bundle). The “biaxial extensional viscosity” of the resin used for producing the filament bundle is 6.0 × 10 ⁶ poise or more (4.0 × 10 ⁶ poise or more for the resin forming the extruded foam fine filament bundle), Biaxial strain hardening rate α "is 0.40 to 0.60 (0.35 to 0.5 in the case of the resin forming the extruded foamed strip bundle).
It is most desirable to use a resin within the range of 5).
According to the present inventors, the value of the “biaxial strain hardening rate α” of the resin used for producing the extruded foamed strip bundle is 0.70 (0.6 for the resin constituting the extruded foamed strip bundle). We have confirmed the possibility of obtaining certain resins.

In addition, a point to be noted in the production apparatus and production conditions for obtaining the extruded foamed strip bundle of the present invention is to increase the "flowing pressure of the foamable composition" and suppress the "foaming in the extrusion die". It is a device for doing. First, the "ultra high molecular weight component" described below, which is the greatest feature of the resin that constitutes the foam of the present invention
The heat stabilizer added to the resin in order to suppress lowering of the molecular weight due to molecular chain scission in the extruder is increased by about 10% from the general standard amount, and the resin temperature in the extruder is 1
It is recommended to try to control the temperature of the extruder so that it does not exceed 95 ° C., and to select an extruder screw having a small stress on the resin molecular chain. Furthermore, the taper angle (θ) of the extrusion die attached to the tip of the extruder
Is preferably adjusted to about 40 ° to 60 °, which has the effect of increasing the “flow pressure of the foamable composition” and suppressing the “foaming in the extrusion die”, and also increasing the swell of the extruded foam strip to extrude. By reducing the bubble diameter in the direction as much as possible, the compressive stress in the extrusion direction of the extruded foam strips is reduced to weaken the anisotropy of the compression stress, and the large swell makes the extruded foam strips larger in diameter. This has the effect of increasing the contact pressure between adjacent extruded foam strips and increasing the fusion force between the extruded foam strips. Also, the taper angle (θ) of the extrusion die
When the value exceeds 60 °, the extruded foam strips are bent and deformed at the time of foaming, and the extruded foam strips are contact-fused only in point form. Therefore, the fusion force between the extruded foam strips is very low. After being dropped, or during cutting, etc., each extruded foamed strip is separated, which poses a serious problem in practical use.

When it is desired to further increase the swell of the extruded foamed strips to further reduce the anisotropy of the compressive stress and further enhance the fusion force between the extruded foamed strips, the extruded foamed strips are bundled. It is desirable to use a resin having a high swell value S of 2.0 or more (the swell value S of the resin used to manufacture the extruded foamed strip bundle is 2.5 or more) as the resin forming the body. In particular, the density of the extruded foam strips is 0.02.
In the case of obtaining an extruded foam strip bundle having a compression stress anisotropy of about 0 g / cm ³ and a wall thickness of 30 mm or more, which has a much higher fusion force between the extruded foam strips, the extruded foam strips can be obtained. The swell value S of the resin forming the focusing body is 2.6 to 3.5.
It is most desirable to adopt a resin having a swell value S of 3.2 to 5.0 for the resin used to manufacture the extruded foamed strip bundle.

The thick extruded foamed strip bundle of the present invention obtained as described above has a thickness of 20 mm or more and a density of 0.005 g / cm ³ or more and 0.04 or more.
g / cm ³ or less, average bubble diameter 0.4 mm or more and 2.0 m
It also satisfies the conditions of m or less and the closed cell rate of 80% or more.

This extruded foamed strip bundle has the above-mentioned JIS
The “minimum value J ₁ of the maximum acceleration at the time of a single drop” measured according to Z0235 shows a value of 80 G or less, and has utility as a cushioning packaging material for the above home electric appliances and the like. or,
According to experiments by the present inventors, the following has been confirmed.
That is, even if the wall thickness satisfies the condition of 20 mm or more,
Density is less than 0.005g / cm ³ , or 0.04g
If it exceeds / cm ³ , the “deterioration degree of cushioning performance K” indicated by the repeated drop evaluation becomes larger than a value of 1.5 and the reliability as a cushioning packaging material is deteriorated, and similarly the closed cell ratio is Even if it is less than 80%, the above-mentioned "buffering performance reduction degree K" exceeds 1.5, and it becomes of no value as a buffer packaging material. If the average cell diameter is less than 0.4 mm, the "compressive stress anisotropy Z", which is the ratio of the compressive stress in the extrusion direction and the thickness direction in the production of the extruded foamed thin fiber bundle, exceeds 1.8. Therefore, it is necessary to pay close attention to the direction of use because the cushioning performance will change significantly depending on the direction of use of the extruded foam strips, and the fusion force between the extruded foam strips will be extremely low, resulting in repeated drop as described above. From the appearance observation of the sample after the evaluation, it is clear that separation of each foamed strip occurs, and similar separation may occur during cutting processing, etc.
The extruded foam strip bundle, which causes such separation, cannot be used as a cushioning packaging material. On the contrary, the extruded foamed strip bundle having a large average cell diameter of more than 2.0 mm has a poor surface appearance and a thick cell film, which makes it uncomfortable to touch and has a low commercial value as a buffer packaging material.

In addition, in addition to the above requirements, the thickness of 30 mm is added to the buffer packaging material for a very fragile product in which the allowable value of "the minimum value J ₁ of the maximum acceleration at the time of one drop" is 65 G or less.
It is desirable to use the above extruded foamed strip bundle. Further, from the viewpoint of more highly retaining the cushioning characteristics of the extruded foamed thin fiber bundle, which is represented by the above-mentioned "minimum value J ₁ of the maximum acceleration at the time of one drop" and "the cushioning performance deterioration degree K", Density of extruded foam strips is 0.015g / cm ³ or more 0.03
It is desirable to select an extruded foam strip bundle having a closed cell rate of 0 g / cm ³ or less and a closed cell rate of 90% or more. Further, FIG. 4 shows the relationship between the ethylene content of the resin constituting the extruded foamed strip bundle of the present invention and the "deterioration degree K of buffer performance" and "thickness recovery rate after compression R" of the extruded foamed strip bundle. FIG.

The vertical axis on the left side represents the "buffering performance deterioration degree K" as 0.
The scale is from 1.0 at 1 interval, the vertical axis on the right side is “the thickness recovery rate after compression R” from 90 to 100 at 1% intervals, and the horizontal axis is the ethylene content Et is from 0.01 to 10% on a logarithmic scale. Up to the scale, the white circles in FIG. 4 indicate the “buffering performance reduction degree K” and the black circles indicate the “thickness recovery rate after compression R”. In the same figure, the line 5 (dashed-dotted line) indicates the level of 1.3 of the "damping performance reduction degree K" which is the standard of the maintainability of particularly severe buffering performance.
"Thickness recovery rate after compression R" is 90% of the thickness in the direction of the wall thickness.
The recovery rate of thickness after 24 hours after compressing and releasing the amount,
If this value is less than 95%, the dimensional recovery of the extruded foam fine-strip bundle is not sufficient after the compression process using a punching blade, which is one of the processing methods of the extruded foam fine-strip bundle, is not sufficient. I can't do it. In FIG. 4, the line 6 (broken line) shows 95% which is the minimum required value of the “thickness recovery rate after compression R”.

Therefore, as is apparent from FIG. 4, the extruded foamed strip bundle of the present invention has a very excellent buffering performance maintainability with a "buffering performance reduction degree K" of 1.3 or less, or a certain specific value. If you want to add dimensional recovery after compression cutting,
It is extremely effective to incorporate the ethylene component into the resin forming the extruded foamed strip bundle. The effect tends to occur when the ethylene content is 0.01%,
% To 4%, the effect is significantly increased, and about 8%, the effect is moderately increased. This fact indicates that the inclusion of an ethylene component requires the buffer packaging field to maintain a high level of repeated buffering performance, and the buffer packaging material processing that requires special processing such as compression processing using a punching blade. It is shown to be useful in the field.

The resin constituting the extruded strip bundle of the present invention has an M _Z of 2 × 10 ⁶ as measured by the GPC method.
Above, especially 2 to 20 (× 10 ⁶ ), and M _Z / M _W is 5 or more, especially 5 to 25 (the resin used for the production of the extruded strip bundle has a Z average molecular weight M _Z of 8 × 10 6. ⁶ or more, especially 8
˜40 (× 10 ⁶ ), and M _Z / M _W, which is the ratio of the Z average molecular weight M _Z and the weight average molecular weight M _W , is 10 or more, particularly 1
It is desirable that the propylene resin is 0 to 50). The Z-average molecular weight M _{Z in} this case emphasizes the contribution of the high-molecular weight component of the resin to the average molecular weight, and the weight-average molecular weight M _W is higher than the Z-average molecular weight M _Z to the average molecular weight of the low-molecular-weight component. It emphasizes contribution. That is, since a high-viscosity polypropylene resin, which is a resin used in the production of conventional extruded strip bundles and plank foams, does not contain a large amount of ultra-high molecular weight components having a molecular weight of 1.0 × 10 ⁷ or more. , Z average molecular weight M _Z should be 8 × 10 ⁶ or more. The presence of this ultra-high molecular weight component has several advantages over the resins used to make conventional extruded strip bundles and plank foams. Firstly, the expression of high "biaxial strain hardening rate α" due to the ease of entanglement of ultra-high molecular weight components, the second is high "biaxial elongational viscosity", and the third is the development of large swell. .

Further, Z average molecular weight M _Z and weight average molecular weight M
The ratio of _W , M _Z / M _W , indicates a wide molecular weight distribution, but M _Z / M _W is 10 or more in the resins used in the production of conventional extruded foam strip bundles and plank foams. The existence of things is unknown. The fact that the value of M _Z / M _W is high indicates that in addition to the presence of the ultra high molecular weight component, a large amount of a low molecular weight component is also contained. Since the shear viscosity does not increase, the screw load of the extruder used for extrusion foaming can be kept low, and further, there is an advantage that a large swell is exhibited.

However, with the current analysis technique, it is difficult to accurately and quantitatively express the presence of the ultrahigh molecular weight component in the resin. Rather, it is more accurate to express the viscoelastic property value of the resin. Is said. The reason why the resin constituting the extruded foamed strip bundle of the present invention is first expressed by the characteristic value of its viscoelasticity is because of the above-mentioned technical background.

The resin constituting the extruded foamed thin fiber bundle of the present invention preferably has a skeleton of a linear polypropylene resin, because the conventional [linear propylene is disclosed in the first publication. Of the biaxial elongation viscosity and the biaxial strain hardening rate α of the resin after being melt-kneaded by an extruder, Since the decrease is small, the properties of the resin once it has been melt-kneaded become important.For the resin used for the production of extruded foam strip bundles, extruded foam can be set without impairing the marginal properties of the resin that can be set. This is because it becomes an ideal resin that can be used for forming a narrow bundle. Also, the above [polypropylene resin having a branched structure having long chain branches mainly at the ends of the linear propylene resin] is estimated from the disclosed production method, and the side to the main chain that is performed by electron beam, radiation, etc. During the chain (branching) bonding process, the main chain is broken at the same time, so the viscosity of the resin as a whole cannot be increased,
It is expected that high biaxial extensional viscosity cannot be achieved by containing an ultrahigh molecular weight component such as a resin used for producing the extruded foamed strip bundle of the present invention. The determination of linearity and branching of the resin skeleton is generally performed using a molecular weight distribution curve created based on data measured by the GPC method, as disclosed in JP-A-6-192460. It can be said that a polymer having a camel-shaped curve in the polymer region of the same curve is branched, and a polymer having no curve is a linear resin.

The polypropylene resin constituting the extruded foamed strip bundle of the present invention is produced, for example, by a two-stage polymerization method using a Ziegler-Natta catalyst using a polymerization tank having a moving fixed bed. What is important as the production conditions at that time is that the titanium-containing compound represented by the following formula (1) and the ester represented by the following formula (2) as a catalyst are ground in a vibrating ball mill at an acceleration of 45 to 55 m. Using a titanium-containing solid component obtained by mixing and grinding at sec ^-2 and a Ziegler-Natta catalyst containing an aluminum component, using hydrogen as a molecular weight control agent, and then using polymerization conditions. First, in the first polymerization step, the polymerization pressure is 30 to 40 kg / cm ² , and the polymerization temperature is 100 to
Polymerization of polypropylene resin having a viscosity (MFR ₁ ) of ₁ to 14 g / 10 minutes at 120 ° C. with an average residence time of the reaction mixture of 1 to 3 hours, and subsequently, in the second polymerization stage, hydrogen as a molecular weight control agent was added. Removal, specifically, with hydrogen at 0.005 mol% or less, polymerization pressure 10 to 20 kgf / c
m ² , polymerization temperature of 40 to 50 ° C., and reaction mixture average residence time of 3 to 5 hours, the polymerization amount in the second polymerization step is 10 to 20 wt% with respect to the total polymerization amount, and the viscosity in the first polymerization step (MFR ₁ ) To a final viscosity (MF of 1/4 to 1/6)
R ₂ ) polypropylene resin.

In particular, the polymerization amount in the second polymerization stage is 10 to 2
The range of 0 wt% is important for the production of the above-mentioned molecular weight, molecular weight distribution, and the associated viscoelastic properties in this production method. When the polypropylene-based resin contains an olefin-based resin other than propylene such as ethylene, a method of adding the above-mentioned olefin-based gas in the second polymerization step and performing polymerization can be used. In this case, since the hydrogen concentration, which is the molecular weight control agent, is lowered to a very low concentration of 0.005 mol% or less, for example, when a large amount of ethylene gas is added, the molecular weight of the resin to be polymerized excessively increases and a large amount of gel component is produced. However, it has been confirmed that continuous polymerization cannot be performed. Therefore, with such a method for producing a resin, only an ethylene content of 8% or less can be actually produced.

TiCl ₃ · nAlCl ₃ (1) (where n is in the range of 0.1 to 0.4) R ₁ —O—CO—R ₂ (2) (Formula) Wherein R ₁ is an alkyl group having 1 to 8 carbon atoms, R ₂ is a phenylalkyl group or a phenyl group having 7 to 14 carbon atoms, and the total number of carbon atoms is a compound having 18 or less. , For example, n-valeric acid ethyl ester,
Phenylbutyric acid ethyl ester. However, the above-mentioned polymerization conditions may vary somewhat depending on the polymerization apparatus used, that is, for example, the shape and structure of the polymerization tank, the size thereof, the shape of the stirring blades, etc. It is recommended to perform some preliminary experiments for reference. The control index in this case is the viscosity at each polymerization stage.

The polypropylene resin constituting the extruded foamed fine fiber bundle of the present invention is a propylene homopolymer or a copolymer of propylene and another olefin resin. Especially, ethylene is preferably used as the olefin resin. The polypropylene-based resin forming the extruded foamed strip bundle of the present invention includes a known crystal nucleating agent for polypropylene-based resin, for example, an aromatic carboxylic acid, for the purpose of rapidly solidifying the resin in the process of solidifying a bubble film. Aluminum salt, dibenzylidene sorbitol,
Substituted dibenzylidene sorbitol, methylene bis (2.
4. -Di-t-butylphenol) acid phosphate sodium salt and / or for the purpose of controlling the generation state of bubbles, for example, inorganic powder such as talc and silicon oxide, organic substances such as zinc stearate and calcium stearate. If necessary, a fine-particle powder, or a cell nucleating agent such as fine powder that decomposes by heating to generate gas, such as citric acid or sodium hydrogen carbonate, may be added. In addition, for example, a necessary amount of a known additive such as an ultraviolet absorber, an antioxidant, an antistatic agent, a colorant, etc. may be added, which means that a conventional extruded foam strip bundle and plank foam can be added. It is the same as the constituent resin.

The "biaxial extensional viscosity" and "biaxial strain hardening rate α" referred to in the present invention are the biaxial extensional viscosity measuring apparatus for lubricating squeeze method, specifically, for example, the liquid biaxial extensional measuring apparatus manufactured by Iwamoto Seisakusho. It is measured using a BE-100 model. The basic measurement conditions are as follows: the sample used is the resin used to manufacture the extruded foamed strip bundles, or the extruded foamed strip bundles have a diameter of 16 ± 1 mm and a thickness of 6.5 ±. Silicone oil [KF968-100C, Shin-Etsu Chemical Co., Ltd.] should be used after being defoamed into a cylindrical shape of 0.5 mm and used as a lubricant interposed between the sample and the measurement plate.
S] was used, and the plate temperature was raised to 200 ±
After stabilizing at 1 ° C., it is carried out under the condition of biaxial elongation strain rate of 0.01 sec ⁻¹ . The biaxial extensional viscosity η ₂ at a biaxial extensional strain of 0.2 out of the obtained measured values is referred to as “biaxial extensional viscosity” in the present invention. On the other hand, the “biaxial strain hardening rate α” is the biaxial extensional viscosity η ₁ when the biaxial extensional strain is 0.01 and the biaxial extensional viscosity η when the biaxial extensional strain is 0.2.
₂ is the rate of change α of biaxial extensional viscosity with respect to biaxial extensional strain between two points and is calculated by the following equation (3). α = 0.77 × log (η ₂ −η ₁ ) (3)

The "swell value S" referred to in the present invention is measured by using Capillograph 1C manufactured by Toyo Seiki. The basic conditions for measurement are a diameter of 2.095 mm and a length of 8.0 mm.
First, the resin used for producing the extruded foamed strip bundle is placed in a barrel whose temperature is adjusted to 180 ° C. using a capillary of
Alternatively, after the resin in a state where the extruded foamed strip bundle is defoamed and molded is put in advance and it is confirmed that the resin is sufficiently melted, the above is performed under a constant shear rate (650 sec ^-1 ). Capillary resin (diameter 2.095mm, length 8.0m
m) is extruded, and the above-mentioned resin diameter W in a string-like recovery and expanded state at a position 10 mm below the lower surface of the capillary is measured and calculated by the following equation (4). S = W / 2.095 (4) The "biaxial elongational viscosity", the "biaxial strain hardening rate α" and the "swell value S" were measured within 30 minutes after starting the resin injection. .

M _Z and M _Z / M _W in the present invention are measured by high temperature gel permeation chromatography (GPC), using 150C GPC chromatography manufactured by WATERS, and 1.2.4-tris as a carrier solvent. Chlorobenzene, shodexA manufactured by Showa Denko KK as a column
Use T-80M / S. The solution temperature is 140
C., solution concentration 0.2% (w / v), solvent flow rate 1 ml / min. "MFR" used in the specification of the present application
Is a melt flow rate value measured at a test temperature of 230 ° C. and a test load of 2.16 kgf according to JIS K7210.

The melt tension referred to in the present invention is measured according to the method described in the publication, using Capirograph 1C manufactured by Toyo Seiki. As a basic condition of the measurement, a capillary having a diameter of 2.095 mm and a length of 8.0 mm was used, and powder was first put in a barrel whose temperature was adjusted to 230 ° C.
Alternatively, pelletized resin is packed in the barrel in the same manner as when measuring the swell value S, then the load is applied to the piston and the piston is lowered at a constant speed of 10 mm / min. And pass it over to the feed roll. The tension of the string-shaped resin was measured while increasing the winding speed, and when the string-shaped resin did not break at the winding speed of 78.5 m / min or less, the tension at the same speed of 78.5 m / min was taken as the melt tension. When the string-shaped resin broke at the same speed of less than 78.5 m / min, the tension immediately before the rupture was defined as the melt tension. Also, this measurement is
It was done within 30 minutes.

[0044]

EXAMPLES Next, the present invention will be described in more detail by way of examples. First, the method for measuring the characteristic values of the extruded foamed strip bundles used in Examples and Comparative Examples is shown below. The extruded foamed strip bundles used for evaluation were aged at 40 ° C. after the production of the extruded foamed strip bundles, and the volume change rate of the extruded foam strips after 30 days became 1% or less. The one in the state of being used was used. (1) Thickness of Extruded Foamed Strip Concentrated Body [Measurement Method] The distance between two parallel opposing surfaces along the extrusion direction of the foamed body was measured using a caliper.

(2) Closed cell ratio [Preparation of sample for measurement] A cubic sample having a side length of 20 mm from the center of the cross section of the extruded foamed thin fiber bundle was cut out and used as a measurement sample. However, when the thickness of the extruded foamed strip bundle was less than 20 mm, a cube having the thickness of the extruded foamed strip bundle as one side was cut out and used as a measurement sample. Furthermore, the diameter of the cross section of the extruded foam strip is 3 m.
Those with holes with m or more spheres were marked as "with void phenomenon", the closed cell ratio was not measured, and there was no commercial value as an extruded foamed strip bundle for buffer packaging.

[Measurement Method] In accordance with the method described in ASTM-D2856, the true volume value Vx of the foam measured by an air-comparison hydrometer 930 manufactured by Toshiba BECKMAN Co., Ltd. Calculate the rate, N
The average value of 5 was calculated. S = (Vx-W / [rho]) * 100 / (Va-W / [rho]) (%) Vx: true volume of extruded foamed strip bundle measured by the above method = constituting extruded foamed strip bundle. Sum of the volume of resin and the total volume of cells in the closed-cell portion in the extruded foamed strip bundle (cm ³ ) Va: Apparent extruded foamed strip bundle calculated from the outer dimensions of the extruded foamed strip bundle Body volume (cm ³ ) W: Weight of extruded foamed strip bundle (g) ρ: Density of resin constituting extruded foamed strip bundle (g /
cm ³ )

(3) Average Cell Diameter [Preparation of Measurement Sample] A cross section of the extruded foamed strip bundle, which is perpendicular to the extrusion direction, is cut into a thickness of 5 mm. [Measurement method of average cell diameter] Grid line method A cut surface is enlarged and projected to produce a cell photograph, and a straight line is drawn on the photograph along the direction of the wall thickness t (mm) of the cross section of the extruded foamed strip bundle. The number L of bubbles contacting the straight line is counted, and the average bubble diameter is calculated by the following formula. Average bubble diameter (mm) = 1.626 x (t / L)

(4) The minimum value J of the maximum acceleration in one drop
₁ [Sample preparation for measurement] An extruded foamed strip bundle having a wall thickness defined by the distance between two parallel facing surfaces along the extrusion direction of the foam was cut in the above-mentioned thickness direction, and The two surfaces facing each other have an area such that each static stress, which will be described later, is generated in the extruded foamed strip bundle when a weight is dropped on the one surface.

[Measurement Method] The measurement was carried out according to JIS Z0235 “Dynamic compression test method for cushioning material for packaging”. Static stress is in the range of 0.02 to 0.4 kgf / cm ^{2, and in} the range of 0.02 to 0.1 kgf / cm ² , it is 0.1 to 0.4 kgf in 0.01 kgf / cm ² increments.
/ Cm in the ^second range as a 0.1 kgf / cm ² increments, the area of the extruded foam strips converging member surface which weight falls, or a weight with a built-in accelerometer while adjusting the weight of the weight, free A drop height of 60 cm is dropped onto the surface of the extruded foamed strip bundle for a total of 5 times at intervals of 30 seconds, and the maximum acceleration generated on the weight during the fall is measured by an accelerometer and recorded. The measured value is the maximum acceleration at the time of one drop and 2 to
The average value of the maximum acceleration at the time of the fifth drop is plotted separately on the dynamic shock curve diagram for static stress, and the points are connected with a smooth curve to complete the dynamic shock curve,
From these two curves, the lowest maximum acceleration value within the static stress range is calculated as “minimum value J ₁ of maximum acceleration in one drop” and “minimum maximum acceleration in the second to fifth drops”, respectively. The value J _AV ".

[Evaluation scale] Scale symbol Over 80G × Cannot be used as cushioning packaging for general home electric appliances Over 65G 80G or less △ Can be used as cushioning packaging for general home electrical appliances 65G or less ○ For buffer packaging for fragile home appliances Available

(5) Buffer performance decrease degree K "Buffer performance decrease degree K" was calculated by the following equation.

K = J _AV / J ₁ [Evaluation scale] Scale symbol Use as a cushioning packaging material for applications where the package is subjected to multiple impacts Over 1.5 × Impossible over 1.3 Over 1.5 or less △ Partially possible 1.3 or less ○ Possible

(6) Fusing property between extruded foam strips [Measurement method] After the measurement of the maximum acceleration at the time of the fifth drop, the appearance of the sample was observed. [Evaluation scale] Scale symbol Use for buffer packaging materials Extruded foam strips cannot be separated into two or more × Impossible Extruded foam strips are not separated into two or more but between extruded strips Some peeling is possible △ Some is possible No peeling between extruded foam strips ○ Possible

(7) Thickness recovery rate after compression R [Preparation of sample for measurement] The sample was prepared in the same manner as the sample for measuring the closed cell content. [Measurement Method] First, the thickness (T1) of the measurement sample is measured. The sample for measurement was uniformly compressed in a thickness direction at 90% of the thickness (T1) at a compression speed of 500 mm / min, and then the pressure was released to 20 ± 2 ° C. and relative humidity was adjusted to 65% for 24 hours. After standing still, thickness again (T2)
Is measured, and the thickness recovery rate R after compression is calculated by the following formula, and N = 3
The average value of R = T2 / T1 × 100 (%) [Evaluation scale] Scale symbol Machinability Less than 95% △ Cannot be compressed using a punching blade 95% or more ○ Can be compressed using a punching blade

(8) Compressive stress anisotropy Z [Preparation of sample for measurement] The sample was prepared by the same method as the sample for measuring the closed cell content. [Measurement Method] Measured in accordance with JIS Z0234 “Static compression test method for cushioning material for packaging”, the measurement sample is compressed at 25% of the original thickness at a load speed of 10 mm / min, and measured at that time. The stress Y (kgf / cm ² ) is calculated from the measured value of the load V (kgf) by the following formula. Area of compressed surface of extruded foamed thin fiber bundle: U (cm ² ) Y = V / U In the above measurement, the stress generated on the surface perpendicular to each of the extrusion direction and the thickness direction is the compression stress in the extrusion direction. Y
_E (average value of N = 5), compressive stress in the thickness direction Y _T (N =
5), and the compressive stress anisotropy Z is calculated by the following equation. Z = Y _E / Y _T

[Evaluation scale] Scale symbol Use for cushioning packaging materials More than 1.8 × Not possible More than 1.5 but not more than 1.8 △ Partially possible 1.5 or less ○ Possible

(9) Density of extruded foamed strip bundles [Preparation of sample for measurement] The sample was prepared in the same manner as the sample for measuring the closed cell content. [Measurement method] Measurement was performed according to JIS K6767. [Comprehensive Evaluation] The evaluation was performed as follows according to the evaluation symbols of the above items. Scale symbol Thick plate extruded foamed strip bundle Product value in use even with one item × No × No ○ and △ No × items △ Low All items ○ ○ High

(Production of Resin) Nine types of polypropylene resins were produced by the two-step polymerization method described in the text, with the viscosity (MFR) as a control index. The obtained resins were numbered as resins 1 to 9 and their characteristic values were measured by the measuring method described in the text. The results are shown in Table 1 together with the above management index. Further, the extruded foamed strip bundles obtained in Examples 1 to 17 using these resins 1 to 9 and the extruded foamed strip bundles obtained in Comparative Examples 1 to 6 using resins 3 to 4, respectively. Table 2 shows the characteristic values of the resins to be used. Further, in the method for producing a polypropylene-based resin by the two-step polymerization method described in the text, polymerization was carried out under the condition that a part of the polymerization conditions in the first step and the second step were removed to obtain resins 10 and 11. Further, three commercially available resins 12 to 14 were prepared. Resin 12 is polypropylene resin "E1100" manufactured by Showa Denko KK, resin 1
3 is polypropylene resin "E310" manufactured by Showa Denko KK
0 "and the resin 14 are" PF-815 "manufactured by Highmont Co., Ltd. used in the examples of the above publications. Resin 1
The characteristic values of 0 to 14 were measured and shown in Table 3 together with the viscosity (MFR) which is a control index. Also, resin 1
Table 4 shows the characteristic values of the resins constituting the extruded foamed strip bundles obtained in Comparative Examples 7 to 22 using 0 to 14. The resins 1 to 11 shown in Table 1 and Table 3
MFR ₂ is a value measured using pellets prepared by kneading various additives into a powdery resin polymerized by using an extruder.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

[Table 4]

(Example 1) Resin 1 was fed at a rate of 50 kg per hour into a feed region of a screw type extruder having a barrel inner diameter of 45 mm, and at the same time, 0.02 was added to 100 parts by weight of resin 1. The cell nucleating agent [Cerbon SC-K manufactured by Eiwa Chemical Co., Ltd.] was supplied at a ratio of parts by weight. The barrel temperature of the extruder was adjusted to 190 ° C., and 100 parts by weight of Resin 1 was added to the mixing area provided at the tip of the extruder to add a foaming agent [tetrafluoroethane / ethyl chloride = mixing foaming agent having a molar ratio of 2/8]. 20 parts by weight was injected to obtain a foamable composition in which a melt of Resin 1, a foaming agent and a cell nucleating agent were mixed. The foamable composition was finally uniformly cooled and adjusted to a temperature of 155 ° C. by a cooling device connected to the outlet of the extruder and then adjusted to an extrusion temperature of 155 ° C. having an internal volume of 3.6 liters. The piston of the hydraulic cylinder was retracted and filled in the accumulator while keeping the accumulator pressure at which foaming did not occur. Immediately after the filling is completed, the extrusion holes with a diameter of 1 mm attached to the tip of the accumulator are arranged in a staggered manner, and the distance between the centers of adjacent extrusion holes is 8 mm, and the extrusion holes are 5 rows in the thickness direction and 8 rows in the width direction. The opening plate of the extrusion die provided in 40 pieces in total was opened, and the piston of the hydraulic cylinder was advanced to extrude at a minimum discharge speed at which the foamable composition in the extrusion die did not "foam in the extrusion die". Immediately after extrusion, the extruded extruded foamed strip bundle was sandwiched between the upper, lower, left, and right sides of the roll to be molded.

Using the obtained extruded foamed strip bundle, the density, wall thickness, closed cell ratio, average cell diameter, 1
Observation / measurement / calculation of the minimum value J ₁ of the maximum acceleration at the time of a single drop, the cushioning performance deterioration degree K, the fusion property between extruded foam strips, the thickness recovery rate after compression R, and the compression stress anisotropy Z Was performed and the results are shown in Table 5.

(Examples 2 to 17) Resin, blowing agent injection amount,
Except that the amount of the cell nucleating agent added was changed as shown in Tables 5 and 6, the substantially same production method as in Example 1 was repeated to obtain extruded foam strip bundles. The extruded foamed strip bundles thus obtained were evaluated by the above-described evaluation methods, and the results are shown in Tables 5 and 6. However, the cooling temperature of the resin and the temperature in the accumulator are set to 155 to 155 only when the extruded foamed strip bundle is manufactured by using the resins 5 to 9 containing ethylene (the same applies to the resins 11 and 13 used in Comparative Examples). In the range of 140 ° C, the temperature was set to the lowest temperature at which the resin solidified product did not come out from the die.

From Tables 5 and 6, when the resin forming the extruded foamed strip bundle of the present invention is used, the wall thickness is 20 mm or more, the closed cell ratio is sufficiently high, and the anisotropy of compressive stress is weak.
An extruded foamed strip bundle in which separation does not occur between the extruded foam strips even when subjected to a severe load such as repeated drops, and the "minimum value J ₁ of the maximum acceleration in one drop" is 80 G or less is obtained. It can be seen that, when the wall thickness is 30 mm or more, the extruded foamed strip bundle has a high "cushioning performance" of "minimum value J ₁ of maximum acceleration in one drop" of 65 G or less. Furthermore,
It can be seen that the inclusion of a predetermined amount of the ethylene component imparts maintainability of the buffer performance and dimensional recoverability after compression. The extruded foamed strip bundles of Examples 16 and 17 were sliced on the surface perpendicular to the thickness direction so that the extruded foamed strip bundles obtained in Example 3 had the thicknesses shown in Table 6. It processed and produced.

[0066]

[Table 5]

[0067]

[Table 6]

(Comparative Examples 1 to 6) Substantially the same as Example 1 except that the resin, the amount of the blowing agent injected, the amount of the bubble nucleating agent added, and the diameter of the die extrusion hole were changed to those shown in the manufacturing condition section of Table 7. The same manufacturing method was repeated to obtain extruded foamed strip bundles. In addition, the extruded foamed strip bundle of Comparative Example 1 is the same as that of Example 3.
The extruded foamed strip bundle obtained in (3) was sliced into a surface perpendicular to the thickness direction so as to have the thickness shown in Table 7. The obtained extruded foam strip bundles were evaluated by the method described above, and the results are summarized in Table 7.

According to the results of Table 7, first, the wall thickness is 20 m.
With an extruded foamed strip bundle of less than m, it is not possible to obtain the "minimum value J ₁ of the maximum acceleration at the time of a single drop" that is generally required for home electric appliances, etc. From the standpoint of maintainability, there is an optimum range for the density and closed cell ratio of the extruded foamed thin fiber bundles. Furthermore, the difference in compressive stress and "buffering performance" depending on the direction of use is reduced, and repeated drops are severe. It can be seen that the average bubble diameter of the extruded foamed strip bundle also has an optimum range in order to prevent the separation between the extruded foamed strips even under various loads.

[0070]

[Table 7]

(Comparative Examples 7 to 13) Except for changing the amount of resin and blowing agent injected, the manufacturing method substantially the same as in Example 1 except that the contents shown in the manufacturing condition section of Table 8 were changed. I got a bundle. The obtained extruded foam strip bundle was evaluated by the method described above, and the results are summarized in Table 8. According to the results shown in Table 8, when a commercially available known resin or the like was used, even if the same amount of the cell nucleating agent as in the example was added, voids were generated or the extruded foamed fine particles with an extremely low closed cell ratio were obtained. It can be seen that it is very difficult to obtain only a filament bundle, and it is also very difficult to obtain a fine extruded foamed filament bundle having a thickness of 20 mm or more and having “buffering performance” and the like.

[0072]

[Table 8]

Reference Examples 14 to 22 The same manufacturing method as in Example 1 was repeated except that the resin, the injection amount of the foaming agent, and the addition amount of the foam nucleating agent were changed to those shown in the manufacturing condition section of Table 9. , Respectively, to obtain extruded foamed strip bundles. The extruded foamed strip bundles thus obtained were evaluated by the above-described evaluation methods, and the results are summarized in Table 9. According to the results in Table 9, when using a commercially available known resin or the like, the closed cell ratio cannot be increased to 80% or more even if the amount of the cell nucleating agent added is increased for the purpose of increasing the closed cell ratio. Compressive stress and "buffer performance"
It is understood that a large anisotropy occurs in the sheet, and further, a load such as repeated dropping causes separation between the extruded foam strips, and the thickness of the extruded foam strip bundle also becomes 20 mm or less.

[0074]

[Table 9]

[0075]

EFFECTS OF THE INVENTION The polypropylene resin extruded foam fine strip bundle of the present invention and the method for producing the same have a wall thickness of 20 mm or more and a density of 0.005 g / c.
m ³ or more and 0.04 g / cm ³ or less, average bubble diameter 0.4 mm
It has a condition of 2.0 mm or less and a closed cell rate of 80% or more. In other words, it has a wall thickness of 20 mm or more.
According to IS Z0235 “Dynamic compression test method for cushioning material for packaging”, the “minimum value of maximum acceleration in one drop” measured by dropping a weight from a height of 60 cm indicates a value of 80 G or less. Anisotropy in cushioning performance due to excellent cushioning performance, little deterioration in "buffering performance" even after repeated drop evaluation, no separation between extruded foamed strips, and small anisotropy of compression stress Thus, it is possible to provide an extruded foam strip bundle having a weak strength and an easy cushioning design.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a process of forming an extruded foam strip bundle and a bubble growth process in the vicinity of an extrusion die of an extruder.

FIG. 2 is an explanatory diagram showing the formation of an extruded foamed strip bundle in the vicinity of the extrusion die of the extruder and the growth process of bubbles when the flow pressure of the resin of the polygonal line 3 in FIG. 1 is mechanically increased. .

FIG. 3 is an explanatory diagram showing a difference in “minimum value J ₁ of maximum acceleration in one drop” of a polyethylene resin plank foam depending on the thickness of the foam.

FIG. 4 shows that the extruded foamed strip bundle of the present invention contains ethylene, thereby imparting to the extruded foamed strip bundle a property of maintaining the cushioning performance and a dimensional recovery after performing a certain specific process. It is explanatory drawing which shows that it is possible.

[Explanation of symbols]

A Land area of extrusion die B Tapered area of extrusion die C Tip area of extruder D, F, F'Extrusion foam strip E1, E2, G1, G2 Bubbles of extrusion foam strip bundle Q1, Q2 Extrusion amount of foamed composition P Flow pressure θ Angle of taper of extrusion die J Maximum acceleration I Static stress t20 Dynamic impact curve diagram of polyethylene foam with wall thickness of 20 mm t30 Polyethylene foam with wall thickness of 30 mm Dynamic impact curve diagram t40 Dynamic impact curve diagram of polyethylene foam having a wall thickness of 40 mm K Degree of decrease in cushioning performance K R Thickness recovery rate after compression R Et Ethylene content 1, 2, 3, 3 ′, 3 ”of resin Flow pressure value 4 Vapor pressure value at the system temperature of the foaming agent 5 Line showing the degree of buffer performance decrease K1.3 6 Line showing the thickness recovery rate after compression R95%

Claims (9)

[Claims] 1. An extruded foamed strip bundle in which a large number of polypropylene-based resin extruded foamed strips arranged in parallel are fused to each other on the outer surface thereof.
Biaxial extensional viscosity at an axial extensional strain of 0.2 is 3 × 10 ⁶ po
ise or more and the biaxial strain hardening rate α is 0.25 or more [however, the biaxial strain hardening rate is expressed by the following equation: α = 0.77 × (log η ₂ −log η ₁ ) (where, η ₁ is 2 The biaxial extensional viscosity is 0.01 when the axial extensional strain is 0.01, and η ₂ is the biaxial extensional viscosity when the biaxial extensional strain is 0.2]. the density of the body is at 0.005 g / cm ³ or more 0.04 g / cm ³ or less, with a wall thickness of 20mm or more, the average cell diameter of 0.4
A polypropylene-based resin extruded foamed strip bundle, which has a closed cell ratio of 80% or more and a diameter of at least 2.0 mm. 2. The polypropylene resin extruded foamed strip bundle according to claim 1, wherein the extruded foamed strip bundle has a compressive stress anisotropy Z of 1.8 or less. 3. The polypropylene resin extruded foamed fine fiber bundle according to claim 1, wherein a swell value S of the polypropylene resin is 2 or more. 4. The polypropylene resin extruded foamed strip bundle according to claim 1, wherein the polypropylene resin is a linear resin. 5. The polypropylene-based resin extruded foamed fine fiber bundle according to claim 1, wherein the polypropylene-based resin has an ethylene content of 0.05 to 8 wt%. 6. The Z-average molecular weight of the polypropylene resin measured by GPC method is 2 × 10 ⁶ or more, and
M _Z / which is the ratio of Z average molecular weight M _Z and weight average molecular weight M _W
The polypropylene resin extruded foamed strip bundle according to claim 1, wherein M _W is 5 or more. 7. A strip under pressure at low temperature and low pressure from an extrusion die having a plurality of extrusion holes, which is prepared by kneading a foamable composition containing a volatile foaming agent in polypropylene resin at high temperature and high pressure and then adjusting the temperature. In the method for producing an extruded foamed strip bundle body in which a plurality of extruded foamed strips are fused and integrated with each other by introducing and condensing the extruded foamed strips into a molding device.
The biaxial extensional viscosity at a biaxial extensional strain of 0.2 of the polypropylene resin is 4.5 × 10 ⁶ poise or more,
2 axial strain hardening index alpha is 0.30 or more [However, 2 axial strain hardening rate, the following _{equation: α = 0.77 × (logη 2} -logη 1) ( wherein, eta ₁ biaxial elongation strain 0. Of the polypropylene resin extruded foamed strip, wherein η ₂ indicates the biaxial extensional viscosity when 01 and η ₂ indicates the biaxial extensional viscosity when the biaxial extensional strain is 0.2). Method for manufacturing a bundle. 8. The taper angle of the extrusion die is 40 ° to
The method for producing a polypropylene-based resin extruded foam fine strip bundle according to claim 7, wherein the angle is 60 °. 9. The method for producing a polypropylene resin extruded foamed strip bundle according to claim 7, wherein the temperature of the polypropylene resin and the foamable composition does not exceed 195 ° C. in the production method.