JP2006077218A - Thermoplastic resin extruded foam and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain thermoplastic resin extruded foam having small reduction in closed cell ratio in foam compression, a uniform foam film and a high-quality appearance in foam containing PTFE powder as a foam nucleus-forming agent. <P>SOLUTION: The thermoplastic resin extruded foam is thermoplastic resin foam having 0.4-2.2mm average foam diameter and 10-110kg/cm<SP>3</SP>foam density, is obtained by adding 0.01-1.0 part wt. of polytetrafluoroethylene powder to 100 parts wt. of a thermoplastic resin and has an average particle diameter of the polytetrafluoroethylene powder of ≥0.5μm and smaller than the average foam film thickness of the foam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a thermoplastic resin containing polytetrafluoroethylene (hereinafter referred to as PTFE) powder, which is usefully used for buffer packaging materials for industrial products, heat insulating materials for houses, sports material core materials for body boats, and the like. The present invention relates to an extruded foam and a method for producing the same.

In producing the plastic foam, but the blowing agent is used, in view of the recent ozone depletion and global warming, in the hydrocarbon blowing agent is from chlorofluorocarbon-based blowing agent _(C 3 ~C ₆₎ foaming agent It is being converted. In the production of thermoplastic resin foams by extrusion foaming, a method of adding a cell nucleating agent is generally used for the purpose of adjusting the cell diameter. As well-known cell nucleating agents, talc, mica, silica, calcium silicate, fat Group metal salts. When foaming with a hydrocarbon-based foaming agent, since the boiling point of the foaming agent is generally higher than that of the chlorofluorocarbon-based foaming agent, the bubble diameter becomes larger than that of the chlorofluorocarbon-based foaming agent. Therefore, in order to obtain a foam having the same cell diameter and the same cell diameter, a large amount of a cell nucleus forming agent is required, and an increase in the content of the foam causes a decrease in the physical properties of the foam.

As a method for obtaining a foam having a uniform fine cell diameter with a small amount of addition, there is a method of adding polytetrafluoroethylene (Patent Document 1) (Patent Document 2). However, the average cell diameter of the foam obtained by the method of Patent Document 1 is as very small as 0.16 to 0.35 mm, which is smaller than the cell diameter of a general plate-like extruded foam. Therefore, the added polytetrafluoroethylene particle diameter of 5 to 40 μm is larger than the cell membrane thickness of the plate-like extruded foam. Since the PTFE powder added to the thermoplastic resin is hardly bonded at the interface with the resin, the interface between the resin and the PTFE powder in the cell membrane is very easy to peel off. If PTFE powder having a large particle diameter is present in the cell membrane, the interfacial separation is liable to cause a decrease in cell membrane strength or a continuous cell formation due to the cell membrane breakage, leading to a decrease in physical properties of the foam. In particular, when the foam is compressed, the influence is great. Patent Document 2 discloses a fluororesin in which the total frequency of particles having a particle diameter of 0.1 to 0.5 μm is at least 50% by volume and the total frequency of particles having a particle diameter of 5 μm or more is 40% by volume or less. A foaming nucleating agent characterized by comprising a powder is disclosed. However, the nucleating agent for foaming has a wide particle size distribution and is prone to agglomeration due to its own weight or external pressure, so that it is difficult to handle and the particle size is difficult to control, and when added to the resin, the kneading strength of the extruder Since the dispersion level of the agglomerated particles varies depending on the number of particles, there is a problem that it is difficult to adjust the bubble diameter of the foam. Moreover, although the Example of patent document 2 has an average bubble diameter as small as 0.2-0.5 mm, there exists a problem that a uniform bubble diameter cannot be obtained when an average bubble diameter is enlarged further.
Japanese Patent No. 2908973 Japanese Patent No. 3457543

  According to the present invention, in a foam to which PTFE powder is added as a cell nucleating agent, a decrease in compression recovery due to the compression of the foam is suppressed by suppressing a decrease in the closed cell ratio due to the rupture of the foam film during the compression of the foam. An object of the present invention is to provide a thermoplastic resin extruded foam having a uniform bubble diameter and a good appearance.

As a result of intensive studies to solve the above problems, the present inventors have used PTFE powder having a specific average particle diameter as a cell nucleus forming agent, and have a specific average cell diameter and foam density. The present inventors have found that the above-mentioned problems can be solved by using an extruded foamed plate-like foam, and have made the present invention.
That is, the present invention is as follows.
(1) A thermoplastic resin extruded foam having an average cell diameter of 0.4 to 2.2 mm and a foam density of 10 to 110 kg / m ³ , wherein the polytetrafluoroethylene powder is the thermoplastic resin 100. The polytetrafluoroethylene powder has an average particle size of 0.5 μm or more and less than 1 times the average cell thickness of the foam. A thermoplastic resin extruded foam.
(2) The average cell diameter is 0.7 to 2.0 mm, the foam density is 35 to 110 kg / m ³ , and the average particle size of the added polytetrafluoroethylene powder is 3 μm or more, The thermoplastic resin extruded foam according to (1), wherein the thermoplastic resin extruded foam has a size of less than 0.5 times the average cell membrane thickness.
(3) The thermoplastic resin extruded foam according to (2), wherein the polytetrafluoroethylene powder has an average particle size of 3 to 5 μm.
(4) The polytetrafluoroethylene powder is polymerized by a suspension polymerization method or a bulk polymerization method, and is subjected to a calcination treatment, according to any one of (1) to (3) Thermoplastic resin extruded foam.
(5) The method for producing a thermoplastic resin extruded foam according to any one of (1) to (4), wherein a hydrocarbon having 3 to 6 carbon atoms is used as the foaming agent.
(6) The method for producing an extruded foam of a thermoplastic resin according to (5), wherein the foaming agent is normal butane.

  The extruded foam of the thermoplastic resin to which the PTFE powder of the present invention is added has a uniform cell membrane and a good appearance, and even when the foam is compressed, the closed cell ratio is reduced due to the membrane rupture. It has the performance that the compression recovery property of a foam does not fall by suppressing.

The present invention will be specifically described below, particularly focusing on preferred embodiments thereof.
Examples of the thermoplastic resin in the present invention include polyethylene homopolymers such as polystyrene, high density polyethylene, medium density polyethylene, low density polyethylene, and linear low density polyethylene, polypropylene homopolymer, polybutene homopolymer, and ethylene-vinyl acetate. Examples thereof include a copolymer, an ethylene-propylene copolymer, an ethylene-butene copolymer, an ethylene-butene-propylene copolymer, an ethylene-acrylic acid copolymer, an aliphatic polyester, and an aliphatic aromatic polyester. These resins can be used alone or in combination as appropriate.

  Examples of the blowing agent in the present invention include aliphatic hydrocarbons such as propane, n-butane, i-butane, n-pentane, i-pentane, and hexane, cyclic aliphatic hydrocarbons such as cyclobutane and cyclopentane, and 1-chloro. And halogenated hydrocarbons such as -1,1-difluoroethane and chloroethane. Furthermore, nonflammable foaming agents such as carbon dioxide, nitrogen, 1,1,1,2-tetrafluoroethane can be mixed with these combustible foaming agents. Moreover, the density of the foam obtained by adjusting the addition amount of these foaming agents can be arbitrarily controlled. Preferred foaming agents are hydrocarbons having 3 to 6 carbon atoms. From the viewpoint of environmental protection such as the recent destruction of the ozone layer and global warming, the foaming efficiency is good and a high foaming ratio is obtained with a small amount of addition. It is preferable in terms of being obtained. Particularly preferred is normal butane. Normal butane has a good foaming property and is quickly dissipated from the foam, and the gas concentration is lowered to less than the lower limit of the combustion range (1.8 vol%) at an early stage, and a safe foam can be made. .

The density of the foam of the present invention is 10 to 110 kg / m ³ . Preferably it is 35-110 kg. When the density of the foam is 10 kg / m ³ or more, a good foam can be obtained from the solubility of the foaming agent in the resin and the foaming efficiency. When the density is 110 kg / m ³ or less, the foam has a large cell diameter and is uniform. Is easy to obtain. When the foam density is 35 to 110 kg / m ³ , the foam appearance is particularly good and particularly preferred.
In the present invention, PTFE powder is used as the cell nucleating agent, but a generally used cell nucleating agent other than PTFE powder may be used in combination as required. Examples of the bubble nucleating agent include an inorganic substance such as talc, a chemical foaming agent that decomposes at an extruder temperature to generate a decomposition gas, or an acid that reacts at that temperature to generate carbon dioxide gas. It's like a mixture of water and alkali.

In the present invention, it is preferable to use a gas permeation modifier in order to prevent volume shrinkage of the foam. Specifically, known gas permeation modifiers, for example, fatty acid glycerides such as palmitic acid glyceride and stearic acid glyceride, fatty acid amides such as oleic acid amide and erucic acid amide, and alkyl fatty acid amides such as stearyl stearic acid amide can be mentioned. . These gas permeation modifiers can be used alone or in combination as appropriate.
Furthermore, in this invention, additives, such as an antistatic agent, antioxidant, a ultraviolet absorber, and a coloring agent, can also be added with respect to mixed resin as needed.
The method for producing a foam of the present invention is to melt and knead a resin, a foaming agent, a cell nucleation agent, and a gas permeation modifier, and other additives under pressure in an extruder, and then to an appropriate foaming temperature. This is because the foamable molten mixture obtained by cooling is extruded under atmospheric pressure through a die attached to the tip of the extruder and foamed.

  As the PTFE powder added to the foam of the present invention, one having an average particle diameter of 0.5 μm or more and less than 1 times the foam average cell membrane thickness is used. The average particle diameter is preferably 3 μm or more and 0.5 times or less of the foam average cell membrane thickness. More preferably, it is 3-5 micrometers. If the average particle size of the PTFE powder is 0.5 μm or more, it is preferable that the PTFE powder can be uniformly dispersed without agglomeration in the foam. Since the PTFE powder and the resin interface in the bubble film are hardly fused, if the average particle size of the PTFE powder is less than 1 times the foam average bubble film thickness, the bubbles should be connected by breaking the film when forming the bubble film. And a foam having a uniform cell diameter can be obtained. In addition, a decrease in closed cell ratio due to film breakage during the compression of the foam is preferably reduced. Furthermore, when the foam average cell membrane thickness is 0.5 times or less, the cell membrane of the PTFE powder-containing portion has a sufficient strength against compression, which is preferable.

The PTFE powder added to the foam of the present invention is preferably a PTFE powder produced by bulk polymerization or suspension polymerization and calcined. The firing condition of the PTFE powder is performed at a melting point of 340 ° C. or higher of the unsintered PTFE powder, and a temperature range of 360 ° C. to 380 ° C. is more preferable. These PTFE powders are less likely to aggregate and disperse with each other. Further, since the particles are hard, there is no change in the particle size after kneading with the resin by an extruder, which is preferable.
The average cell diameter of the foam of the present invention is 0.4 to 2.2 mm. Preferably it is 0.7 mm-2.0 mm. When the average bubble diameter is 0.4 mm or more, a sufficient bubble film thickness can be obtained, so that a foam having a uniform bubble diameter can be obtained without bubbles breaking during foaming. An average cell diameter of 2.2 mm or less is preferred in that the appearance of the foam is good. The addition amount of the PTFE powder of the present invention is 0.01 part by weight to 1.0 part by weight with respect to 100 parts by weight of the thermoplastic resin. Preferably, it is 0.05-1.0 weight part. If it is 0.01 parts by weight or more, it can be stably added to the resin, and a uniform nucleation effect can be obtained. If it is 1.0 parts by weight or less, a nucleation effect commensurate with the amount added can be obtained. Furthermore, the density of PTFE particles in the cell membrane is preferably low. The bubble diameter of the foam can be controlled by appropriately adjusting the amount of the bubble nucleating agent added.

EXAMPLES Hereinafter, although this invention is demonstrated based on an Example, the content of this invention is not limited to these Examples. The values shown in the examples are measured by the following method.
(1) Foam density (according to JIS K 6767)
The mass and volume of a product (sample size 20 mm × 20 mm × thickness 25 mm) cut out in the entire thickness direction from each position divided into 5 parts in the width direction of the foam, the density is calculated by the following formula, and the density of 5 points Was the foam density.
Foam density (kg / m ³ ) = foam mass (kg) / foam volume (m ³ )
(2) Average cell diameter of foam A test piece is cut from the center of the foam, and a straight line of L (mm) is drawn on the cut surface along the extrusion direction, the width direction, and the thickness direction of the foam. The number of bubbles in contact with each other was counted, the bubble diameters in the extrusion direction, the width direction, and the thickness direction were calculated by the following formula, and the average value in the three directions was defined as the average bubble diameter (grid line method).
Bubble diameter in each direction (mm) = 1.626 × L / number of bubbles (3) Average particle diameter of PTFE powder For measurement of particle diameter, laser diffraction scattering method using Microtrac FRA (trade name) (manufactured by Nikkiso Co., Ltd.) The particle size of 50% of the integrated value of the particle size frequency was taken as the average particle size.

(4) Measurement of the closed cell ratio of the foam and evaluation of the influence of the closed cell ratio by compression After the foaming gas inside the foam has escaped, the foam that is not compressed and the foam that is compressed 60% in the thickness direction Prepared, left for 24 hours in an environment of 25 ° C., and n by the air pycnometer method described in ASTM-D2856 (manufactured by Tokyo Science Co., Ltd., air comparison specific gravity system 1000 type (trade name) used) = Closed cell ratio was measured and calculated with an average of 5 and evaluated according to the following criteria.
Closed cell ratio (%) = closed cell volume (cm ³ ) / foam apparent volume (cm ³ ) × 100
Compression speed condition: 10 mm / min (closed cell ratio after compression / closed cell ratio before compression) × 100 (%)
(Double-circle): It has 95% or more of the closed cell ratio before compression.
○: It has 90% or more of the closed cell ratio before compression.
X: Less than 90% of the closed cell ratio before compression.
(5) Average bubble film thickness It computed with the following formulas.
Average cell membrane thickness (mm) = 0.46 × average cell diameter (mm) × (foam density / resin density)
Density unit: (kg / m ³ )

[Example 1]
Low-density polyethylene (density 921 kg / m ³ , MI = 2.9 g / 10 min) is bubbled into 100 parts by weight of this resin at a feed rate of a screw-type extruder having a barrel inner diameter of 150 mm at a speed of 900 kg / hour. Supplied with 0.2 parts by weight of PTFE powder (average particle size 3.9 μm, KTL-4N (trade name) manufactured by Kitamura Co., Ltd.) and 0.8 parts by weight of gas permeation modifier (stearic acid monoglyceride) as a nucleating agent did. The barrel temperature of the extruder was adjusted to 190 ° C to 210 ° C, and 7 parts by weight of a foaming agent consisting of 100% by weight of n-butane was injected into 100 parts by weight of this resin from a foaming agent injection port attached to the tip of the extruder. Then, it was mixed with the molten resin composition to obtain a foamable molten mixture. After cooling this foamable molten mixture to 108 ° C. with a cooling device attached to the outlet of the extruder, it was cooled at room temperature and atmospheric pressure from an orifice plate having an average thickness of about 4.0 mm and an opening shape of about 226 mm wide. foamed continuously extruded into the atmosphere, and molded while adjusting the drawing speed of the resin foam, thickness 62 mm, width 560 mm, length 1000 mm, an average cell diameter 1.0 mm, the plate-like density 38 kg / ^{m 3} A resin foam was obtained. After the foaming agent concentration inside the resin foam became 1.8 vol% or less, the foam thickness was compressed by 60%, and the closed cell ratio before and after compression was evaluated. The results are shown in Table 1.

[Example 2]
Low density polyethylene (density 921 kg / m ³ , MI = 3.2 g / 10 min) was added to the same extruder as in Example 1 at a rate of 800 kg / hr as a cell nucleating agent with respect to 100 parts by weight of this resin. It was supplied together with 0.5 part by weight of PTFE powder (average particle size 4.2 μm, KTL-8N (trade name) manufactured by Kitamura Co., Ltd.) and 0.6 part by weight of a gas permeation modifier (stearic acid monoglyceride). Adjusting the barrel temperature of the extruder to 190 ° C. to 210 ° C., 9.65 parts by weight of the foaming agent composed of 100% by weight of n-butane from the foaming agent injection port attached to the tip of the extruder with respect to 100 parts by weight of the resin. Was injected and mixed with the molten resin composition to obtain a foamable molten mixture. After cooling this foamable molten mixture to 108 ° C. with a cooling device attached to the outlet of the extruder, it was cooled at room temperature and atmospheric pressure from an orifice plate having an average thickness of about 3.6 mm and an opening shape of about 278 mm wide. foamed continuously extruded into the atmosphere, and molded while adjusting the drawing speed of the resin foam, thickness 52 mm, width 560 mm, length 1000 mm, an average cell diameter 0.9 mm, the plate-like density 70 kg / ^{m 3} A resin foam was obtained. After the foaming agent concentration inside the resin foam became 1.8 vol% or less, the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[Example 3]
Low-density polyethylene (density 921 kg / m ³ , MI = 2.7 g / 10 min) was fed into the same extruder as in Example 1 at a rate of 650 kg / hr as a cell nucleating agent with respect to 100 parts by weight of this resin. 0.04 parts by weight of PTFE powder (average particle size: 3.9 μm, KTL-4N (trade name) manufactured by Kitamura Co., Ltd.) and 1.0 part by weight of a gas permeation modifier (stearic acid monoglyceride) were supplied. The barrel temperature of the extruder was adjusted to 190 ° C to 210 ° C, and 7 parts by weight of a foaming agent consisting of 100% by weight of n-butane was injected into 100 parts by weight of this resin from a foaming agent injection port attached to the tip of the extruder. Then, it was mixed with the molten resin composition to obtain a foamable molten mixture. After cooling this foamable molten mixture to 109 ° C. with a cooling device attached to the outlet of the extruder, it was cooled at room temperature and atmospheric pressure from an orifice plate having an average thickness of about 2.5 mm and an opening shape of about 280 mm width. foamed continuously extruded into the atmosphere, and molded while adjusting the drawing speed of the resin foam, thickness 52 mm, width 590 mm, length 1000 mm, an average cell diameter 1.7 mm, the plate-like density 27 kg / ^{m 3} A resin foam was obtained. After the foaming agent concentration inside the resin foam became 1.8 vol% or less, the same evaluation as in Example 1 was performed. The results are shown in Table 1.

[Example 4]
The added PTFE powder has an average particle size of 9.6 μm (KTL-10N (trade name) manufactured by Kitamura Co., Ltd.), the amount added is 0.25 parts by weight, and the average cell diameter of the obtained foam is 1.0 mm. Except that, a plate-like resin foam was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

[Comparative Example 1]
The added PTFE powder has an average particle diameter of 20.4 μm (KTL-20N (trade name) manufactured by Kitamura Co., Ltd.), the amount added is 0.25 parts by weight, and the average cell diameter of the obtained foam is 0.9 mm. Except that, a plate-like resin foam was produced in the same manner as in Example 1 and evaluated. The results are shown in Table 1.

[Comparative Example 2]
The added PTFE powder has an average particle diameter of 20.4 μm (KTL-20N (trade name) manufactured by Kitamura Co., Ltd.), the amount added is 0.8 parts by weight, and the average cell diameter of the obtained foam is 0.5 mm. Except that, a plate-like resin foam was produced in the same manner as in Example 2 and evaluated. The results are shown in Table 1.

[Comparative Example 3]
The added PTFE powder has an average particle size of 20.4 μm (KTL-20N (trade name) manufactured by Kitamura Co., Ltd.), the added amount is 0.02 parts by weight, and the average cell diameter of the obtained foam is 1.4 mm. Except that, a plate-like resin foam was produced in the same manner as in Example 3 and evaluated. The results are shown in Table 1.

  INDUSTRIAL APPLICABILITY The present invention is suitably used for buffer packaging materials such as industrial products, heat insulating materials such as houses, and sports equipment core materials such as body boats.

Claims (6)

An extruded foam of a thermoplastic resin having an average cell diameter of 0.4 to 2.2 mm and a foam density of 10 to 110 kg / m ³ , wherein the polytetrafluoroethylene powder is added to 100 parts by weight of the thermoplastic resin. 0.01 to 1.0 part by weight is added, and the polytetrafluoroethylene powder has an average particle size of 0.5 μm or more and less than 1 times the average bubble film thickness of the foam. Plastic resin extruded foam. The average cell diameter is 0.7 to 2.0 mm, the foam density is 35 to 110 kg / m ³ , and the average particle size of the added polytetrafluoroethylene powder is 3 μm or more, the thermoplasticity The thermoplastic resin extruded foam according to claim 1, which has a size less than 0.5 times the resin foam foam average cell membrane thickness.   The thermoplastic resin extruded foam according to claim 2, wherein the polytetrafluoroethylene powder has an average particle size of 3 to 5 µm.   The thermoplastic resin extrusion according to any one of claims 1 to 3, wherein the polytetrafluoroethylene powder is polymerized by a suspension polymerization method or a bulk polymerization method, and is subjected to a firing treatment. Foam.   The method for producing a thermoplastic resin extruded foam according to any one of claims 1 to 4, wherein a hydrocarbon having 3 to 6 carbon atoms is used as the foaming agent.   The method for producing an extruded foam of a thermoplastic resin according to claim 5, wherein the foaming agent is normal butane.