JP2008056863A - Polypropylene-based resin foamed sheet and molded article obtained by thermally molding the foamed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polypropylene-based resin foamed sheet which can suitably be used for obtaining molded articles excellent in the visibility of articles received therein because of having excellent transparency. <P>SOLUTION: This polypropylene-based resin foamed sheet is characterized by having a density of 90 to 180 kg/m<SP>3</SP>, a basis weight of 0.15 to 0.40 g/m<SP>2</SP>, one to four foamed cells in the thickness direction, and a total light transmittance of >60% measured according to JIS K 7361-1. The molded article having the characteristics is obtained by thermally molding the polypropylene-based resin foamed sheet. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polypropylene resin foam sheet that can be suitably used to obtain a molded article that is lightweight and excellent in transparency.

  Foamed sheets made of thermoplastic resins are generally lightweight, have good heat insulation and buffering properties against external stress, and can be easily obtained by heat forming such as vacuum forming. It is widely used in applications such as food containers, cushioning materials, heat insulating materials, and automotive parts. In particular, due to the recent increase in awareness of environmental impact reduction, the light weight of foam sheets has come to attract attention again.

  Among these thermoplastic resin foam sheets, a foam sheet using a polypropylene resin as a base resin is superior in heat resistance and oil resistance compared to conventional polystyrene resin foam sheets due to the characteristics of the base resin. Therefore, a molded body obtained by thermoforming a polypropylene resin foam sheet has been frequently used in recent years (for example, Patent Documents 1 and 2). On the other hand, depending on the articles accommodated in the molded body (for example, articles such as food and electronic parts), the molded body is required to have transparency so that the articles accommodated from the outside of the molded body can be discriminated in addition to the design properties. However, these polypropylene resin foam sheets are inferior in transparency because they have fine cells and a large number of cells, so that the molded product is also inferior in transparency, and it is difficult to distinguish the contained articles. there were.

Then, compared with the conventional polypropylene-type resin foam sheet, while making the magnitude | size of the foam cell in a sheet comparatively large, the polypropylene-type resin foam sheet with few numbers of foam cells is proposed (patent documents 3 and 4). . The foamed sheet is different in appearance and texture from the conventional polypropylene resin foamed sheet, and it looks like it is made of ice and gives a refreshing feeling. The range of choices can be expanded. However, although there is a design property that it seems to be made of ice, the transparency is not sufficient depending on the distribution ratio and basis weight of the size of the foamed cells in the foamed sheet. Furthermore, in the foamed sheet, it was difficult to reduce the density so as to contribute to lightness, that is, to obtain a foamed sheet having a high foaming ratio, because of the chemical foaming method using the decomposable foaming agent. .
Japanese Patent No. 2521388 JP-A-11-228726 JP 2000-103893 A JP 2004-99701 A

  An object of the present invention is to provide a polypropylene-based resin foam sheet that can be suitably used to obtain a molded article that is low in density, light in weight, and excellent in transparency, and that is excellent in visibility of an article to be stored. .

  As a result of intensive studies to solve such problems, the present inventors have reached the present invention.

That is, the present invention
The density is 90 to 180 kg / m ³ , the basis weight is 0.15 to 0.40 g / m ² , the number of foamed cells in the thickness direction is 1 to 4, and all measured according to JIS K 7361-1 A polypropylene resin foam sheet (Claim 1) having a light transmittance of more than 60%, and a molded product obtained by thermoforming the polypropylene resin foam sheet according to Claim 1 (Claim 2). )
About.

  The polypropylene resin foam sheet of the present invention provides a lightweight and excellent molded article by regulating the density, basis weight, number of foam cells in the thickness direction, and total light transmittance of the foam sheet. Can be suitably used.

The density of the polypropylene-based resin foam sheet of the present invention is preferably ^{90~180kg / m 3, 100~150kg / m} 3 and more preferably. If the density of the polypropylene resin foam sheet is less than 90 kg / m ³ , the appearance of the resulting molded product may be impaired, and if it is greater than 180 kg / m ³ , the resulting molded product may be less lightweight. There is a tendency to be inferior in heat insulation and buffering properties.

The basis weight of the polypropylene-based resin foam sheet of the present invention is more it is preferably ^{0.15kg / m 2 ~0.40kg / m 2} , a 0.18kg / m ² ~0.38kg / m ² preferable. If the basis weight of the foam sheet is less than 0.15 kg / m ² , the strength of the resulting molded product tends to be insufficient, and if the basis weight is greater than 0.40 kg / m ² , the resulting molded product will be lightweight. It tends to be inferior and cost increases.

  The number of foam cells in the thickness direction of the polypropylene resin foam sheet in the present invention is preferably 1 to 4, more preferably 1 to 3. When the number of foamed cells in the thickness direction is less than 1, there are many portions that are not partially foamed, and the function as a foamed body such as heat insulation and buffering may be remarkably inferior. Further, when the number of foamed cells in the thickness direction is more than 4, the resulting molded article tends to be inferior in transparency.

  In addition, the measurement of the number of foam cells in the thickness direction of the polypropylene resin foam sheet in the present invention is performed by cutting the foam sheet in the width direction (direction perpendicular to the flow direction) and measuring 10 points at equal intervals in the width direction. The number of foam cells in the sheet thickness direction at each measurement point is measured, and the average value is adopted as the number of foam cells in the thickness direction.

  The total light transmittance measured by JIS K 7361-1 of the polypropylene resin foam sheet in the present invention is preferably more than 60%, and more preferably 65% or more. When the total light transmittance of the foamed sheet is 60% or less, the molded product obtained by thermoforming the foamed sheet tends to be inferior in transparency, and the visibility of an article accommodated in the molded product tends to be inferior. .

  The closed cell ratio in the polypropylene resin foam sheet of the present invention is preferably 60% or more, and more preferably 70% or more. If the closed cell ratio of the foamed sheet is less than 60%, the heat insulating properties and rigidity of the resulting molded product may be impaired.

  The polypropylene resin of the base resin used in the production of the polypropylene resin foam sheet of the present invention is a linear polypropylene resin (hereinafter referred to as “raw material polypropylene” because of its high melt viscosity and excellent foamability. Resin (which may also be referred to as a “system resin”) by irradiating an electron beam to introduce a long chain branch (for example, HMS-PP, etc. manufactured by Basel Co., Ltd.), or an isoprene monomer for a raw material polypropylene resin And a modified polypropylene resin obtained by melt-kneading a radical polymerization initiator. In particular, a modified polypropylene resin obtained by melting and kneading a raw material polypropylene resin, an isoprene monomer and a radical polymerization initiator is easy to manufacture, can be manufactured at a low cost, and is suitable for manufacturing a foam sheet. It is preferable from the viewpoint of easy adjustment of the viscosity.

Furthermore, the polypropylene resin used for the production of the polypropylene resin foam sheet of the present invention can be reduced in density (high expansion ratio) in the production of the foam sheet, and has a high closed cell ratio even at a low density. The equilibrium compliance J _eo measured at 210 ° C. is preferably less than 1.2 × 10 ⁻³ Pa− ¹ , and preferably less than 1.0 × 10 ⁻³ Pa− ^1. More preferred.

The equilibrium compliance J _eo in the present specification is measured by the following method using a rheometer SR-2000 manufactured by Rheometric Scientific. After sandwiching a molded product of polypropylene resin having a thickness of 3 mm between two parallel disks and maintaining the temperature at 210 ± 1 ° C. and sufficiently melting, the interval between the parallel disks is adjusted to 1.4 mm, Remove the resin protruding from the disc. Next, at time t = 0, one disk is rotated with respect to the other so that the stress σ _{c applied} to the sample is kept at a constant value of 100 N / m ² , and the amount of strain at that time for 300 seconds γ (t) is measured over time. Further, the creep compliance J (t) defined by the following formula is plotted against the time t from the start of giving the stress σ _c .

After a sufficient time has elapsed, the creep compliance J (t) has a linear relationship with the time t, and the equilibrium compliance J _eo is shown in the plot of the creep compliance J (t) and time t. Is given as an intercept when extrapolating a portion giving a linear relationship at time t = 0.

  As the raw material polypropylene resin, a copolymer obtained by copolymerizing another monomer that can be copolymerized with propylene may be used. Examples of other monomers that can be copolymerized with propylene include ethylene, butene-1, α-olefin, cyclic olefin, diene monomer, and vinyl monomer. Among these monomers, ethylene or butene-1 is preferable from the viewpoint of being inexpensive.

  The molecular weight (weight average molecular weight) of the raw material polypropylene resin is preferably in the range of 50,000 to 2,000,000 from the viewpoint of industrial availability, and 100,000 to 1,000,000 from the point of being inexpensive. More preferably, it is in the range.

  If necessary, other resins or rubber components may be added to the polypropylene resin as the base resin of the polypropylene resin foam sheet of the present invention within a range not impairing the effects of the present invention. The amount of other resin or rubber component added to the polypropylene resin as the base resin varies depending on the type of this resin or the type of rubber component, and may be within the range not impairing the effects of the present invention as described above. In general, it is preferably 25 parts by weight or less with respect to 100 parts by weight of the polypropylene resin.

  In addition, the polypropylene resin as the base resin may further include an antioxidant, a metal deactivator, a phosphorus processing stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, a fluorescent whitening agent, a metal, if necessary. Stabilizers such as soap and antacid adsorbents, or additives such as crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, flame retardants, antistatic agents, etc. You may add within the range which does not impair.

  The polypropylene resin foam sheet of the present invention is produced by an extrusion foaming method using a volatile foaming agent as described below. By using a volatile foaming agent as the foaming agent, the low density (high foaming ratio) foamed sheet of the present invention can be obtained. The polypropylene resin foam sheet according to the present invention is obtained by, for example, melting and kneading a polypropylene resin and a volatile foaming agent in an extruder, adjusting the resin temperature to the foaming temperature in the extruder, and then forming a circular die having an annular lip. Used, extruded from the lip of the die to atmospheric pressure to obtain a cylindrical foam, and then drawn and cooled by molding with a cooling cylinder (mandrel) while taking up the cylindrical foam, and then cut open Manufactured by the method of forming. The basis weight of the polypropylene resin foam sheet can be adjusted by changing the discharge amount of the melt-kneaded product and the take-up speed of the cylindrical foam.

  Examples of the volatile blowing agent include aliphatic hydrocarbons such as propane, butane, isobutane, pentane, hexane, and heptane, alicyclic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane, chlorodifluoromethane, dichloromethane, Halogenated hydrocarbons such as dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane, chloroethane, dichlorotrifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, perfluorocyclobutane, nitrogen, carbon dioxide, air Inorganic gas etc. are mention | raise | lifted etc., You may use them in combination of 1 type, or 2 or more types.

  The addition amount (kneading amount) of the volatile foaming agent varies depending on the type of foaming agent and the target density of the foamed sheet, but is 1.0 to 10 parts by weight with respect to 100 parts by weight of the polypropylene resin composition. Preferably, 1.5 to 8 parts by weight is more preferable.

  Furthermore, in the production of a polypropylene resin foam sheet, an inorganic powder or a decomposable foaming agent may be used in combination as a cell nucleus forming agent for appropriately controlling the number of cells in the polypropylene resin foam sheet.

Examples of the inorganic powder that can be used include talc, calcium carbonate, barium sulfate, silica, titanium oxide, clay, aluminum oxide, bentonite, and diatomaceous earth.
As the decomposable foaming agent, for example, an inorganic carbon dioxide generator alone or a combination with a weak acid can be used. Examples of the inorganic carbon dioxide generator include ammonium carbonate and ammonium bicarbonate, as well as carbonates or bicarbonates of alkali metals or alkaline earth metals. Moreover, these may be a mixture of two or more. Weak acids include oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, itaconic acid, citraconic acid, adipic acid, formic acid, acetic acid, propionic acid, butyric acid, stearic acid, oleic acid, caprylic acid, enanthic acid, capron Acid, valeric acid, lactic acid, tartaric acid, citric acid, phthalic acid, benzoic acid, benzenesulfonic acid, toluenesulfonic acid, chloroacetic acid, diglycolic acid and other organic acids, boric acid and other inorganic acids, and acidic potassium tartrate and other acidic salts Is mentioned. Moreover, these may be a mixture of two or more.

  The amount of the cell nucleating agent used as necessary is not particularly limited as long as the effect of the present invention is not impaired. Usually, the inorganic powder is added to 100 parts by weight of the polypropylene resin composition. If it is, it is preferable that it is 0.05-2 weight part, 0.08-1.5 weight part is more preferable, and 0.005-0.01 weight part is preferable if it is a decomposable foaming agent. 005 to 0.008 parts by weight are more preferable. In addition, it is easy to control the amount added, and from the viewpoint of manufacturing stability, it is preferable to use inorganic powder.

  The polypropylene-based resin foam sheet in the present invention can obtain a molded article that is lightweight and excellent in transparency by a commonly used thermoforming method. Examples of thermoforming include plug molding, match molding, straight molding, drape molding, plug assist molding, plug assist reverse draw molding, air slip molding, snapback molding, reverse draw molding, free drawing molding, plug Examples of the method include AND ridge molding and ridge molding, but match mold molding is preferable because of excellent mold shape forming properties.

  The molded product obtained by using the polypropylene resin foam sheet of the present invention is lightweight and excellent in transparency, so it is excellent in environmental compatibility and is required for food containers and electronic component containers that require visibility of stored articles. Can be used.

  EXAMPLES Next, although this invention is demonstrated in detail based on an Example, this invention is not limited to this Example.

  Evaluation methods in Examples and Comparative Examples are as follows.

(Measurement of density of foam sheet)
Measurement was performed in accordance with JIS-K6767.

(Foaming ratio of foam sheet)
The density value of the base resin for the foam sheet was calculated by dividing by the density value of the obtained foam sheet.

(Measurement of foam sheet thickness)
The obtained foamed sheet was cut out in parallel to the width direction, the thickness was measured with calipers at 10 equally spaced points in the width direction, and the average value was taken as the thickness of the foamed sheet.

(Measurement of basis weight of foam sheet)
The obtained foamed sheet was calculated from the area and weight of a strip cut out to a width of 100 mm in parallel with the width direction.

(Measurement of closed cell ratio of foam sheet)
In accordance with the method described in ASTM D2856, measurement was performed with an air pycnometer.

(Measurement of the number of foam cells in the foam sheet)
The obtained foam sheet is cut in the width direction, 10 points at equal intervals in the width direction are taken as measurement points, the number of foam cells in the sheet thickness direction at each measurement point is measured, and the average value is foamed in the sheet thickness direction. The number of cells.

(Measurement of total light transmittance of foam sheet)
From the obtained foamed sheet, a sample of 100 mm square was cut out at three arbitrary positions (generally at the center and both ends) in the width direction, and a haze meter (NDH2000, manufactured by Nippon Denshoku Industries Co., Ltd.) was used to JIS K 7361-1. Based on this, total light transmittance was measured, and an average value of three points was calculated.

(Preparation of molded article for evaluation)
Using a match mold for obtaining a molded body having the shape shown in FIG. 1 (the shape of the opening of the molded body is a square shape of 120 mm × 120 mm around the flange, a height of 35 mm, and a mold clearance of 1.2 mm). The polypropylene resin foam sheets (500 mm × 500 mm) obtained in the examples and comparative examples were subjected to heat molding by a small vacuum / pressure forming machine (FVS500P, manufactured by Wakisaka Engineering Co., Ltd.) to obtain a molded product for evaluation. In addition, in heating of a foam sheet, it performed with the infrared heater with which a molding machine is equipped, and it adjusted so that the surface temperature of a foam sheet might be 135-145 degreeC.

(Transparency evaluation of molded products)
As shown in FIG. 2, the transparency of the obtained molded body was expressed by capital letter letters (font: Gothic full-width, letter size: 12 points, letter color: black, letters: AZ) printed on white paper. ) Can be recognized at a distance of 30 cm through the molded body. In addition, the illumination intensity of the evaluation place measured with the illuminance meter (The Sato Corporation make, LX-100) was about 900 lux.
○: All characters can be confirmed, and the molded article is excellent in transparency.
X: There are characters that cannot be confirmed, and the molded article is inferior in transparency.

(Strength evaluation of molded body)
The strength of the obtained molded product was evaluated by measuring the strength of the molded product using a digital force gauge (manufactured by Imada Co., Ltd., DPS-5R) by the following method.
FIG. 3 is a conceptual diagram illustrating a method for evaluating the strength of a molded body. As shown in FIG. 3, the center of the molded body flange is sandwiched between the aluminum compression jigs 5 while the molded body 3 is erected, and the center of the flange of the molded container is compressed by 10 mm. The maximum load sensed by the digital force gauge 4 connected to the tool 5 was defined as the strength of the molded body. The contact width between the jig 5 and the molded body 3 was 10 mm, and the compression speed was 10 mm / second.
The following evaluation was performed from the strength of the compacts measured for 10 compacts.
(Circle): The average value of a molded object strength is 2.0 N or more.
X: The average value of the strength of the compact is less than 2.0N.

The manufacturing method of the base resin for polypropylene resin foam sheets used in the examples is as follows.
[Method for producing base resin for foam sheet]
100 parts by weight of a propylene homopolymer (manufactured by Prime Polymer Co., F113G) and 0.2 part of t-butyl peroxybenzoate (manufactured by Nippon Oil & Fats Co., Ltd., perbutyl Z) are stirred with a ribbon blender. By feeding the mixed compound to a twin screw extruder using a metering feeder, supplying 0.4 parts of isoprene from the middle of the extruder using a liquid pump, and melt-kneading in the twin screw extruder. The pellet of the modified polypropylene resin composition for foam sheet manufacture was obtained.
The equilibrium compliance J _eo measured at 210 ° C. of the modified polypropylene resin composition was 0.8 × 10 ⁻³ Pa- ¹ .
The twin-screw extruder was the same-direction twin-screw type, the screw diameter was 44 mmφ, and the maximum screw effective length (L / D) was 38. The set temperature of the cylinder part of the twin screw extruder was 180 ° C. up to the isoprene press-in position, 200 ° C. after the isoprene press-in position, and the screw rotation speed was set at 150 rpm.

(Example 1)
A 65-90 mmφ tandem extruder was prepared by mixing 100 parts by weight of the base resin for foam sheet and 0.5 parts by weight of talc (high filler # 11 made by Matsumura Sangyo Co., Ltd.) as a bubble nucleating agent with stirring with a ribbon blender. And melted in a first stage extruder (65 mmφ) set at a cylinder temperature of 200 ° C., and then 1.6 parts by weight of isobutane as a foaming agent is injected into 100 parts by weight of the base resin for the foam sheet. After mixing, it is cooled in a second stage extruder (90 mmφ) set at 160 ° C., and discharged from a circular die (caliber 75 mmφ) at a discharge rate of 50 kg / hr under atmospheric pressure, an outer diameter of 200 mm and a main body length of 250 mm. While being molded with a cooling cylinder, it is drawn and cooled while being drawn at a take-up speed of 4.7 m / min to obtain a cylindrical foam, and this is opened with a cutter. The foam sheet of 630mm was produced.
Using the obtained foamed sheet, a molded article for evaluation was produced and evaluated by the above method. Table 1 shows the physical properties of the foam sheet and the evaluation results of the molded product.

(Example 2)
A foamed sheet was produced in the same manner as in Example 1 except that the take-up speed was 3.8 m / min.
Using the obtained foamed sheet, a molded article for evaluation was produced and evaluated by the above method. Table 1 shows the physical properties of the foam sheet and the evaluation results of the molded product.

(Example 3)
A foamed sheet was produced in the same manner as in Example 1 except that the amount of isobutane injected and mixed was 3.0 parts by weight.
Using the obtained foamed sheet, a molded article for evaluation was produced and evaluated by the above method. Table 1 shows the physical properties of the foam sheet and the evaluation results of the molded product.

(Comparative Example 1)
Except for blending 0.4 parts by weight of sodium bicarbonate-citric acid-based air conditioner master batch (Daiblo Seika Co., Ltd., Die-Blow SSC PE-M D20 (AL) N) instead of talc as a bubble nucleating agent A foam sheet was produced in the same manner as in Example 1.
Using the obtained foamed sheet, a molded article for evaluation was produced and evaluated by the above method. Table 1 shows the physical properties and molded body evaluation results of the foam sheet.

(Comparative Example 2)
A foamed sheet was produced in the same manner as in Example 1 except that the take-up speed was 13.2 m / min.
Using the obtained foamed sheet, a molded article for evaluation was produced and evaluated by the above method. Table 1 shows the physical properties of the foam sheet and the evaluation results of the molded product.

(Comparative Example 3)
A foamed sheet was produced in the same manner as in Example 1 except that the amount of isobutane injected and mixed was 0.7 parts by weight.
Using the obtained foamed sheet, a molded article for evaluation was produced and evaluated by the above method. Table 1 shows the physical properties of the foam sheet and the evaluation results of the molded product.

  With the foam sheet used in the examples, a molded article having a high expansion ratio and excellent transparency could be obtained. On the other hand, the foamed sheet of Comparative Example 1 is inferior in the transparency of the molded product obtained with a large number of foamed cells, and the foamed sheet of Comparative Example 2 is inferior in the strength of the molded product obtained because of its low basis weight. The foamed sheet of 3 is inferior in strength of the obtained molded product because of its low foaming ratio (in other words, the basis weight must be increased in order to maintain strength, that is, inferior in lightness). Thus, the good molded object like an Example was not able to be obtained.

The figure which shows the molded object in an Example and a comparative example The figure which shows the transparency evaluation method of the molded object in an Example and a comparative example The figure which shows the strength evaluation method of the molded object in an Example and a comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Molded object upper drawing 2 Molded object AA sectional drawing 3 Molded object 4 Paper on which the character was printed 5 Evaluator's viewpoint 6 Molded object strength measuring jig 7

Claims (2)

The density is 90 to 180 kg / m ³ , the basis weight is 0.15 to 0.40 g / m ² , the number of foamed cells in the thickness direction is 1 to 4, and all measured according to JIS K 7361-1 A polypropylene resin foam sheet characterized by having a light transmittance of more than 60%.   The molded object obtained by heat-molding the polypropylene resin foam sheet of Claim 1.

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