JPH0598058A - Propylene resin foam and its production - Google Patents

Abstract

PURPOSE:To provide the title foam which can be properly produced over a wide range of foaming temp. and exhibits an excellent flexibility over a range of from a high to a low expansion ratio while overcoming defects occurring in a conventional extruded propylene resin foam prepd. from a noncrosslinked propylene resin. CONSTITUTION:A noncross-linked resin component comprising 97-55wt.% propylene resin having long-chain branches and a drawdown of 60m/min or lower and 3-45wt.% linear ultralow-density polyethylene is melt mixed with a blowing agent and extruded under a low pressure thus giving the title foam.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a propylene resin foam and a method for producing the same, and more particularly to a propylene resin foam having excellent flexibility and a method for producing the same.

[0002]

2. Description of the Related Art As a method for producing a foam having a long shape, an extrusion foaming method in which a thermoplastic resin is melt-kneaded with a foaming agent in an extruder and then extruded at a low pressure to foam is widely adopted. ..

In the extrusion foaming method of an olefinic resin, when a melt-kneaded product of a resin and a foaming agent is extruded from the extruder under a low pressure, the foaming agent in the melt-kneaded product expands to foam. However, when the temperature of the resin is raised, the viscosity drops sharply, and the resin cannot hold the foaming agent and escapes from the resin to become a foam of open cells. Conversely, the resin temperature must be increased to increase the viscosity of the resin. If it is lowered, the crystallization of the resin will proceed, and as a result, the foam will not foam sufficiently and uniformly, and the surface of the foam will become uneven. It is necessary to perform viscoelasticity that can be retained at a temperature that the resin has. The temperature range in which viscoelasticity suitable for foaming is obtained differs depending on the type of resin, and this temperature range is generally called the foaming suitable temperature range.

[0004]

However, the viscoelasticity of the propylene resin, which has a higher degree of crystallinity than that of low density polyethylene and the like, greatly changes due to a slight temperature change, and the foaming suitable temperature range is very narrow. It is extremely difficult to carry out extrusion foaming while maintaining the resin temperature within such a narrow temperature range, and when the extrusion foaming temperature fluctuates and goes out of the foaming suitable temperature range, the foamed part has an open cell structure. However, it was difficult to obtain a foam having good and uniform properties as a whole. Conventionally, in the case of a non-crosslinked propylene-based resin, a relatively good foam can be obtained only when the density is a low expansion ratio of more than 0.2 g / cm ³ or when the density is 0.013 g / cm ^3. It has a high expansion ratio of less than.

The above-mentioned problems are considered to be caused by the high crystallinity of the propylene-based resin, and the density of the propylene-based resin is 0.
The reason why an extruded foam with a low expansion ratio of more than 2 g / cm ³ can be obtained relatively well is that the ratio of the resin is larger than the amount of the foaming agent. It is considered that this is because the temperature can be set to be considerably higher than that. The density is 0.013 g / cm ³
The reason why it is possible to obtain a foam having a high expansion ratio of less than 1 relatively well is as follows.

Generally, the olefin resin being foamed during extrusion foaming is subjected to an external cooling operation using a cooling means, thereby solidifying the cell walls to obtain a good foam. However, since propylene-based resin has a higher degree of crystallinity than low-density polyethylene, the amount of heat generated during crystallization is large. This heat hinders the cooling and thus the solidification of the cell walls, and destroys or deforms the cells of the propylene-based resin in the process of foaming. Therefore, by adding a large amount of foaming agent to foam, the heat of vaporization (expansion heat) of the foaming agent is used to drastically lower the temperature of the propylene-based resin in the process of foaming, thereby promoting the solidification of the cell wall. .. Further, a large amount of foaming agent has a function of delaying the crystallization of the resin in the extruder. As a result, the foam can be obtained relatively well. However, in this case, since the foaming agent needs to be blended in a large amount, the resulting foam inevitably has a density of 0.013 g /
It has a high expansion ratio of less than cm ³ . Also in this case, the temperature range suitable for foaming is only about 0.6 ° C.

The inventors of the present invention have earnestly studied in view of the fact that only non-crosslinked propylene-based resins can produce extruded foams having a high expansion ratio or a low expansion ratio. By doing so, it was found that even a propylene-based resin extruded foam having a density of 0.2 to 0.013 g / cm ³ can be easily produced,
I filed an application earlier (Japanese Patent Application No. 3-86168).

However, since the propylene-based resin has a higher degree of crystallinity and a higher hardness than the ethylene-based resin, the propylene-based resin foam obtained by the above method is more brittle and less flexible than the ethylene-based resin foam. However, when the propylene resin is a propylene homopolymer, there is a drawback that the flexibility is further lowered.

The present invention has been made in view of the above points,
An object of the present invention is to provide a propylene-based resin foam which is useful as a cushioning material and has excellent flexibility, and a method for producing the same.

[0010]

That is, the propylene-based resin foam of the present invention has long-chain branching and draw-down property (however, the draw-down property means that the molten propylene-based resin heated to 230 ° C. is melt-indexed). It is extruded into a cord shape at a constant speed of 10 mm / min from a nozzle of a kusa (caliber 2.095 mm, length 8 mm), and then the cord-like material is fed by a feed roll positioned above the tension detecting pulley located below the nozzle. After passing, the winding speed of the winding roll is gradually increased while being wound by the winding roll to cut the string-like object, and the winding speed of the string-like object at the time of this cutting is referred to. ] Of 60 m / min or less and a linear ultra-low density polyethylene mixed resin, and the content of the linear ultra-low density polyethylene in the mixture is 3 to 45% by weight. It is characterized in that a non-crosslinked propylene resin is used as the base resin.

Further, in the method for producing a propylene resin foam of the present invention, the above-mentioned specific non-crosslinked propylene resin having a long chain branch and a foaming agent are melt-kneaded in an extruder and then attached to the tip of the extruder. It is characterized by being extruded and foamed under low pressure through a die. In the present invention, a propylene homopolymer is particularly preferable as the propylene resin having a drawdown property of 60 m / min or less.

The base resin constituting the foam of the present invention is a mixture of a propylene resin having a drawdown property of 60 m / min or less and a linear ultra-low density polyethylene. The drawdown property is 60 m / min. The propylene resin below
Unlike ordinary propylene resins, the main chain must have long-chain branching. Such a special resin is a normal crystalline linear propylene-based resin (usually having a weight average molecular weight of 100,000 or more), and is a component which is atactic component and / or isotactic but is not crystalline. (Hereinafter, this resin is referred to as "normal propylene-based resin" in order to distinguish it from the propylene-based resin having a drawdown property of 60 m / min or less used in the present invention.) (Temperature: room temperature to about 120 ° C.) is mixed and heated to 120 ° C. or lower to bond an atactic or / and non-crystalline isotactic component as a branched chain to the main chain of a normal propylene resin. Etc., and is usually considered to have a branched structure mainly having long chain branches at the ends.

The usual propylene-based resin used to obtain the propylene-based resin used in the present invention may be either a propylene homopolymer or a copolymer of propylene and a small amount of olefin other than propylene. In the case of a copolymer, the olefin other than propylene copolymerized with propylene may be ethylene or a carbon number of 4 to 1
0 α-olefins, including 1
They may be used alone or in combination of two or more. Examples of the α-olefin having 4 to 10 carbon atoms include 1-butene, isobutylene, 1-pentene and 3-methyl-1-.
Butene, 1-hexene, 3,4-dimethyl-1-butene, 1
-Heptene, 3-methyl-1-hexene and the like.

Examples of the low temperature decomposition type peroxide include di (s-butyl) peroxydicarbonate and bis (2-
Ethoxy) peroxydicarbonate, dicyclohexyl peroxydicarbonate, di-n-propylperoxydicarbonate, di-n-butylperoxydicarbonate, diisopropylperoxydicarbonate,
Examples thereof include t-butyl peroxy neodecanoate, t-amyl peroxy neodecanoate and t-butyl peroxypivalate.

The propylene-based resin having a drawdown property of 60 m / min or less is prepared by substituting the inside of the reaction vessel with an inert gas such as argon while stirring the above-mentioned ordinary propylene-based resin in a reactor equipped with a stirrer. Then, the above-mentioned peroxide is usually added in an amount of 5 to 50 mmol per kg of the resin, and the mixture is heated to about 120 ° C., preferably about 70 to 105 ° C. while continuing stirring to react (usually 30 to 120 minutes), and thereafter. , Obtained by stopping the reaction. In stopping the reaction, a reaction terminator such as methyl mercaptan is introduced into the reaction vessel, or the reaction product is heated at 130 to 150 ° C.
A method of heating for about 20 to 40 minutes or the like is adopted.

The drawdown property used in the present invention is 60 m /
The propylene-based resin of not more than the portion may be a propylene homopolymer or a propylene copolymer, but is particularly preferable in the case of a propylene homopolymer because the effect is particularly remarkable.

The propylene resin used in the present invention preferably has a drawdown property of 30 m / min or less, particularly preferably 15 m / min or less. This drawdown property is 2
The molten propylene-based resin heated to 30 ° C. is extruded from a melt indexer (caliber 2.095 mm, length 8 mm) at a constant speed of 10 mm / min into a string shape, and then the string-like material is placed under the tension of the nozzle. After passing through the feed roll located above the detection pulley, the take-up roll winds up while the winding speed of the take-up roll is gradually increased to cut the string-like object. It refers to the winding speed of the material.

The drawdown property can be adjusted by the number and length of the long chain branches. Generally speaking, the larger the number of long chain branches and the longer the branch length, the more this value tends to decrease. Therefore, in order to obtain a desired propylene resin having a drawdown property, it is necessary to set the reaction conditions in consideration of these things. In the case of having no long-chain branch, or having a branch that is too short or too little, or in the case of a normal propylene-based resin, the drawdown property exceeds 60 m / min. Extrusion foaming is performed using such ordinary propylene-based resin
Even if an attempt is made to obtain a foam of about 0.2 to 0.013 g / cm ³ , the obtained foam will have many corrugations and surface irregularities, and will have no commercial value.

The above VLDPE is similar in molecular structure to a general linear low-density polyethylene (hereinafter referred to as LLDPE), but LLDPE is prepared by a method such as having more short chain branches than LLDPE. It is a soft polyethylene having a lower crystallinity than that of LLDPE and general high-pressure low density polyethylene (hereinafter referred to as LDPE). VLDPE usually has a density of 0.870 to 0.914 g / cm ³ , but a density of 0.88.
It is preferably from 0 to 0.910 g / cm ³ .

The base resin that constitutes the foam of the present invention is a non-crosslinked propylene-based resin which is a mixture of the propylene-based resin having a drawdown property of 60 m / min or less and the VLDPE. The content of VLDPE in the resin must be 3 to 45% by weight.
The content of LDPE is preferably 5 to 40% by weight, and particularly 1
0 to 30% by weight is preferable. Drawdown property is 60m /
Minute difference in propylene-based resin and VLDPE, the difference in melting point is large (the difference between the two is approximately 35 ° C. or more), and thus the difference in viscosity at the foaming temperature is large. Therefore, the content of VLDPE in the base resin is large. Is more than 45% by weight, the proportion of cells communicating with each other inside the obtained foam increases. If it is less than 3% by weight, the effects of improving brittleness and flexibility cannot be obtained.

Incidentally, regarding the drawdown property,
Generally, when the VLDPE content in the mixed resin is about 3% by weight or less, the drawdown property of the mixed resin maintains the drawdown property of the propylene resin in the present invention, but as the VLDPE amount increases, , Its value tends to be high. In the present invention, it is desirable that the drawdown property of the mixed resin also maintains the range of the drawdown property of the propylene resin. Therefore, the higher the content of VLDPE, the lower the drawdown property of the propylene resin mixed therewith. It is desirable that

The drawdown property used in the present invention is 60 m /
Propylene-based resin of less than a minute, its crystallization temperature +15 ℃
It is preferable that the half-crystallization time is 800 seconds or more, and particularly preferably 1000 seconds or more. A crystallization rate measuring device can be used for the measurement of the semi-crystallization time. To measure the semi-crystallization rate, first place the support holding the film-like sample in the air bath of the crystallization rate measuring instrument to completely melt the sample, then melt the melted sample together with the support and crystallize the sample. Immersion in an oil bath maintained at a temperature of + 15 ° C so as to block the optical path between the light source and the optical sensor, and a constant amount of light is always detected by the optical sensor until the melted sample solidifies again. Thus, the voltage of the light source is adjusted to obtain the voltage-time curve as shown in FIG. When the voltage when the voltage in this curve has a constant value is V ₀ , the time until the voltage becomes 1/2 V ₀ is the half-crystallization time.

The foam of the present invention usually has a density of 0.6 to 0.0.
It is obtained by extrusion foaming with a target of 18 g / cm ³ and a thickness of 0.1 to 150 mm. As a method for obtaining the foamed product of the present invention, after the above-mentioned base resin and the foaming agent are melt-kneaded in an extruder, a method of extruding the melt-kneaded product under low pressure through a die attached to the tip of the extruder to foam is adopted. To be done. In particular, in order to obtain a sheet-like foam, a circular die having an annular lip is used, and a tube-like foam is obtained by extrusion foaming from the lip of this die, and then the tube is cut open to form a sheet. Is usually adopted.

As the foaming agent, an inorganic foaming agent, a volatile foaming agent, a decomposable foaming agent or the like can be used. Carbon dioxide, air, nitrogen, etc. can be used as an inorganic foaming agent. Volatile blowing agents include propane, n-butane, i
-Butane, pentane, aliphatic hydrocarbons such as hexane, cyclobutane, cycloaliphatic hydrocarbons such as cyclopentane,
Halogenated hydrocarbons such as trichlorofluoromethane, dichlorodifluoromethane, dichlorotetrafluoroethane, methyl chloride, ethyl chloride and methylene chloride can be used. As the decomposition type foaming agent, azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate or the like can be used. These foaming agents can also be used by appropriately mixing them. The amount of the foaming agent used varies depending on the type of the foaming agent, the desired expansion ratio, etc., but for example, the standard of the amount of the foaming agent used to obtain a foam having a density of about 0.2 to 0.013 g / cm ³ is The amount of volatile foaming agent is about 0.5 to 25 parts by weight (converted to butane) per 100 parts by weight of the base resin. Further, the standard of the amount of the foaming agent used to obtain a foam having a density of more than 0.09 g / cm ³ is about 0.1 to 10 parts by weight for the inorganic foaming agent per 100 parts by weight of the base resin. In the case of a mold blowing agent, it is about 0.1 to 5 parts by weight.

In the method of the present invention, a cell regulator may be further added to the melt-kneaded product of the base resin and the foaming agent. Examples of the bubble control agent include inorganic powders such as talc and silica, acidic salts of polyvalent carboxylic acids, and reaction mixtures of polyvalent carboxylic acids with sodium carbonate or sodium bicarbonate.
It is preferable to add about 13 parts by weight or less of the cell regulator to 100 parts by weight of the base resin (except when a large amount of the inorganic filler is contained in the resin). If necessary, a heat stabilizer, an ultraviolet absorber, an antioxidant,
It is also possible to add additives such as colorants.

In the present invention, the base resin may previously contain an inorganic filler in an amount of 40% by weight based on the total weight. Examples of the inorganic filler include talc, silica,
Examples thereof include calcium carbonate, clay, zeolite, alumina, barium sulfate and the like. Their average particle size is 1 to 70
It is preferably μm. When a large amount of such an inorganic substance is contained, the obtained foam has improved heat resistance and can reduce the calories burned during incineration.

[0027]

EXAMPLES The present invention will be described in more detail with reference to examples. The physical properties of the resins used in Examples and Comparative Examples are shown in Tables 1 and 2. In addition, in the examples and comparative examples, the total amount of the foaming agent and the cell regulator is 100% by weight based on the total amount of these and the mixed resin (only the comparative example 5 is a single resin).
Is the weight percentage. A melt indexer and a melt tension tester type II manufactured by Toyo Seiki Seisakusho Co., Ltd. were used in combination to measure the drawdown property and melt tension of the resin used, and the half-crystallization time was measured by Kotaki Corporation. A crystallization rate measuring instrument MK-801 manufactured by K.K. was used.

In measuring the drawdown property, 7
Since 8.5 m / min is the measurable upper limit, 78.5 m / min
When the string-like material was not cut in minutes, it was expressed as "78.5 m / min or more". Further, the tension (gf) detected by the pulley immediately before the string-like object was cut was read and used as the melt tension. However, when the string-like material was not cut at the winding speed of 78.5 m / min, the tension detected by the pulley at this speed was taken as the melt tension.

[0029]

[Table 1]

[0030]

[Table 2]

The base resin shown in Table 3 was mixed with a foaming agent (isobutane) and a cell regulator (talc) in the ratio shown in the same table in an extruder (screw diameter 50 mm, L / D = 46) and melt-kneaded. After that, at the foaming temperature shown in the same table, the inner surface of the tubular foam is extruded into a tube shape from a circular die with a diameter of 75 mm (die diameter) and a clearance (lip clear) of 0.3 mm attached to the tip of the extruder. Was taken in contact with a cooling mandrel (mandrel diameter 200 mm), and then this tubular foam was cut open in the extrusion direction to obtain a sheet. The extrusion conditions at this time are shown in Table 3, and the properties of the foamed sheet obtained are shown in Table 4.

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

As described above, in the method of the present invention, although the base resin is a non-crosslinked propylene-based resin, the foaming temperature range of the base resin is wide, so that the extrusion foaming temperature can be controlled. It is easy to use a non-crosslinked propylene resin as a base resin, and it is possible to obtain a propylene resin foam which is homogeneous in its entirety and has excellent properties. Further, the foam obtained by the method of the present invention has no shrinkage or corrugation, and the brittleness, which is a drawback of the foam using the non-crosslinked propylene-based resin as a base resin, is improved, and the foam has excellent flexibility.

[Brief description of drawings]

FIG. 1 is a voltage-time curve obtained by crystallization rate measurement.

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[Procedure amendment]

[Submission date] October 20, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction content]

The propylene-based resin having a drawdown property of 60 m / min or less is prepared by substituting the inside of the reaction vessel with an inert gas such as argon while stirring the above-mentioned ordinary propylene-based resin in a reactor equipped with a stirrer. Then, the above-mentioned peroxide is usually added in an amount of 5 to 50 mmol per kg of the resin, and the mixture is stirred up to about 120 ° C, preferably 70 to 105 ° C.
It is obtained by heating to a certain degree to react (usually for 30 to 120 minutes) and then stopping the reaction. In stopping the reaction, a reaction terminator such as methyl mercaptan may be introduced into the reaction vessel, or the reaction product may be added in an amount of 130 to 150.
A method of heating to about 40 ° C. for 20 to 40 minutes is adopted.
Whether long-chain branch exists in the molecular chain of propylene resin
Can be confirmed by the following method. That is, extension flow
Measuring device (eg Rheometrics extensional flow measurement
Equipment: Propylene-based using the product name RER-9000)
A measurement sample is made from resin and the strain of this sample
Elongational viscosity (poise) at time (sec- ¹ ) and time
Graph the relationship with (seconds). Smell on this graph
The long-chain branch and the propylene-based resin
Propylene resin that does not include propylene resin
Ren resin has a large extensional viscosity curve with time.
However, with propylene-based resin that does not have long chain branching
Is the slope of the elongational viscosity curve smaller with time?
Can be distinguished. Above Rheometrics
Is it the measurement result by the long flow measuring device (RER-9000)?
A long-chain branched propylene-based resin and a long-chain branched
Elongational Viscosity of Strainless Propylene Resin at Strain Rate
The graph of FIG. 2 shows the relationship between degrees and time. Gu
Curve A in the rough shows a propylene resin with long chain branching.
The curve B shows a propylene-based resin having no long chain branching.
Show. From this graph, the propylene type with long chain branching
With resins, the slope of the extensional viscosity curve increases with time.
On the other hand, with propylene-based resin that does not have long chain branching
Shows that the slope of the elongational viscosity curve decreases with time.
I understand. The measurement sample and measurement conditions are as follows.
Is. ・ Measurement sample size and shape: length 30 mm, diameter 5
mm columnar strain rate: 1.0 second ■ -1 ・ Measurement temperature: Base resin melting point + 20 ° C (however, the melting point is
Material resin 1 to 5 mg by differential scanning calorimeter at 10 ° C / min
Of the endothermic peak of the DSC curve obtained when the temperature is raised by
Temperature. )

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Added

[Correction content]

FIG. 2 is a graph showing a relationship between elongational viscosity and time at a strain rate of a propylene resin having a long chain branch and a propylene resin having no long chain branch.

[Procedure 3]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 2

[Correction method] Added

[Correction content]

[Fig. 2]

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Claims (4)

[Claims] 1. A linear ultra-low density in a mixture of a propylene-based resin having a long chain branching and a drawdown property of 60 m / min or less and a linear ultra-low density polyethylene. Polyethylene content is 3 ~
A propylene-based resin foam characterized by using a non-crosslinked propylene-based resin of 45% by weight as a base resin [however, the drawdown property means that the molten propylene-based resin heated to 230 ° C. Nozzle (caliber 2.0
(95 mm, length 8 mm) at a constant speed of 10 mm / min in the form of a string, and then the string is passed through a feed roll located above the tension detecting pulley located below the nozzle and then wound up. While winding with a roll, gradually increase the winding speed of the winding roll to cut the string-like object,
It refers to the winding speed of the string-like material at the time of this cutting. ]. 2. The propylene-based resin foam according to claim 1, wherein the propylene-based resin having a drawdown property of 60 m / min or less is a propylene homopolymer. 3. A straight-chain ultra-low density in the mixture, which comprises a mixture of a propylene-based resin having a long-chain branch and a drawdown property of 60 m / min or less and a straight-chain ultra-low-density polyethylene. Polyethylene content is 3 ~
A propylene-based resin foam characterized in that 45% by weight of a non-crosslinked propylene-based resin and a foaming agent are melt-kneaded in an extruder and then extruded under low pressure through a die attached to the tip of the extruder to foam. Manufacturing method [however,
The draw-down property is a melt indexer nozzle (caliber 2.095
mm, length 8 mm) at a constant speed of 10 mm / min in the form of a string, and then the string is passed through a feed roll located above the tension detecting pulley located below the nozzle and then wound up. While winding with a roll, the winding speed of the winding roll is gradually increased to cut the string-like material, and the winding speed of the string-like material at the time of this cutting is referred to. ]. 4. The method for producing a propylene-based resin foam according to claim 4, wherein the propylene-based resin having a drawdown property of 60 m / min or less is a propylene homopolymer.