JP2898460B2 - Propylene resin foam sheet for molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a foamed propylene resin sheet for molding.

[0002]

2. Description of the Related Art As a method for producing a long-sized foam or a sheet-like foam for forming a container or the like, a thermoplastic resin is melt-kneaded with a foaming agent in an extruder, and then subjected to low pressure. An extrusion foaming method of extruding and foaming is widely used.

In the extrusion foaming method of an olefin resin, when a melt-kneaded product of a resin and a foaming agent is extruded under a low pressure from an extruder, foaming is performed by expanding the foaming agent in the melt-kneaded material. However, if the temperature of the resin is increased, the viscosity drops sharply, the resin cannot retain the foaming agent, escapes from the resin and becomes a foam of open cells, and conversely, the resin temperature is increased to increase the viscosity of the resin. If the temperature is lowered, crystallization of the resin proceeds, and as a result, the foam does not foam sufficiently and uniformly, and the foam surface becomes uneven. For this reason, extrusion foaming needs to be performed at a temperature at which the resin has sufficient viscoelasticity so that a sufficiently uniform foaming can be performed and a foaming agent can be held in the resin. The temperature range in which viscoelasticity suitable for foaming is obtained differs depending on the type of resin, and this temperature range is generally referred to as a foaming suitable temperature range.

[0004]

However, the propylene-based resin having a higher degree of crystallinity than low-density polyethylene or the like greatly changes the viscoelasticity of the resin due to a slight temperature change, and has a very narrow temperature range for foaming. It is very 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 deviates from the appropriate foaming temperature range, the foamed portion has an open-cell structure. And the surface became uneven, and it was difficult to obtain a foam having good overall and uniform properties. Conventionally, in the case of a non-crosslinked propylene-based resin, a relatively good foam can be obtained only at a low expansion ratio having a density exceeding 0.2 g / cm ³ or at a density of 0.013 g / cm ^3. It has a high expansion ratio of less than.

[0005] 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 not higher than 0.
Extruded foams having a low expansion ratio of more than 2 g / cm ³ can be obtained relatively favorably because the ratio of the resin is larger than the amount of the foaming agent. It is considered that the reason is that the temperature can be set to a considerably higher temperature. The density is 0.013 g / cm ³
The reason why a foam having a high expansion ratio of less than 1 can be obtained relatively favorably is as follows.

In general, a foaming olefin-based resin in the process of extrusion foaming is subjected to a cooling operation from the outside by using a cooling means, whereby the cell wall is solidified to obtain a good foam. However, since the propylene-based resin has a higher degree of crystallinity than low-density polyethylene, the calorific value during crystallization is large. This heat hinders the cooling and thus the solidification of the cell walls, and breaks or deforms the cells of the propylene-based resin in the process of foaming.

Therefore, by foaming a large amount of a foaming agent, the temperature of the propylene-based resin in the course of foaming is rapidly lowered by utilizing the heat of vaporization (heat of expansion) of the foaming agent, thereby solidifying the cell wall. Promote. Further, a large amount of the foaming agent has a function of delaying crystallization of the resin in the extruder. As a result, a relatively good foam can be obtained. However,
In this case, the foam obtained necessarily has a high expansion ratio of less than 0.013 g / cm ³ due to the necessity of blending a large amount of a foaming agent. Also in this case, the suitable foaming temperature range is only about 0.6 ° C.

In view of the fact that only extruded foams having a high expansion ratio or a low expansion ratio can be obtained with a propylene resin, the present inventors have found that the use of a propylene resin having a specific drawdown property allows the density to be reduced. 0.3 ~ 0.06g / cm
^{In addition} to finding a method that can be easily manufactured even with the extruded propylene-based resin foam of ³ , the skin thickness, the thickness of the foam, and the number of foam films in the thickness direction have a specific relationship at a specific thickness of the foam. The present inventors have found that a foamed sheet is suitable for thermoforming, and have completed the present invention. An object of the present invention is to provide a foamed propylene-based resin sheet having excellent heat moldability.

[0009]

That is, the foamed propylene resin sheet of the present invention has a skin layer on the surface of a non-crosslinked propylene resin having a long chain branch and a drawdown property of 60 m / min or less. Having a density of 0.3 to 0.06 g / cm ³ and a thickness of 1 to ³ mm,
And between the thickness of the surface skin layer and the average thickness of the bubbles,
The thickness of the surface skin layer / the average thickness of the bubbles ≦ 2, and the number of bubble films in the thickness direction is 2 to 15.

The base resin constituting the foamed sheet of the present invention is a non-crosslinked propylene resin having a long chain branch and a drawdown property of 60 m / min or less, and may be a homopolymer, a block copolymer, or a random copolymer. Any of copolymers may be used,
A propylene copolymer excellent in deep drawability described later is preferred.

In the case of a copolymer, a copolymer of propylene and a small amount of an olefin other than propylene is preferred. Examples of the olefin include ethylene and α-olefins having 4 to 10 carbon atoms. Two or more kinds can be used in combination. Examples of the α-olefin having 4 to 10 carbon atoms include 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-
Methyl-1-hexene and the like.

The α-olefin is preferably contained in the copolymer in an amount of usually not more than 20% by weight, particularly preferably not more than 10% by weight. Particularly, when the α-olefin is ethylene, it is preferably not more than 5% by weight. It is preferable that it is contained in a ratio. The preferred lower limit of the content of these α-olefins in the copolymer is 0.5% by weight for all α-olefins. The copolymer may be a random copolymer or a block copolymer, but is preferably a block copolymer in view of the easiness of forming a long-chain branch, and particularly preferably a propylene / ethylene block copolymer. preferable.

The propylene resin as the base resin of the foamed sheet of the present invention is different from a normal propylene resin,
It must have a long-chain branch in the main chain. Such a special resin is an ordinary crystalline linear propylene resin (usually a weight average molecular weight of 100,000 or more), and further contains an atactic component or / and an isotactic but not crystallized component. (To be distinguished from the propylene resin used in the present invention, this resin is referred to as "normal propylene resin".)
When simply referred to as a propylene-based resin, it means the resin used in the present invention. ) Is mixed with a low-temperature decomposition type (decomposition temperature: about room temperature to about 120 ° C.)
° C or less, and a method in which an atactic or / and non-crystallized isotactic component is bonded to the main chain of a normal propylene-based resin as a branched chain. It is considered to have a branched structure having branches.

The low-temperature decomposable peroxides include di (s-butyl) peroxydicarbonate and bis (2-
Ethoxy) peroxydicarbonate, dicyclohexylperoxydicarbonate, di-n-propylperoxydicarbonate, di-n-butylperoxydicarbonate, diisopropylperoxydicarbonate,
Examples thereof include t-butyl peroxy neodecanoate, t-amyl peroxy neodecanoate, t-butyl peroxy pivalate, and the like.

The propylene resin as the base resin of the foamed sheet of the present invention is obtained by replacing the above-mentioned ordinary propylene resin with an inert gas such as argon while stirring the propylene resin in a reactor equipped with a stirrer. Then, the above peroxide is usually added in an amount of usually 5 to 50 mmol per 1 kg of the resin, and the mixture is heated to about 120 ° C., preferably about 70 to 105 ° C. while continuing to stir to cause a reaction (usually for 30 to 120 minutes). Later, it is obtained by stopping the reaction. In terminating the reaction, a reaction terminator such as methyl mercaptan is introduced into the reaction vessel, or the reaction product is heated to 130 to 150 ° C.
For example, a method of heating for about 20 to 40 minutes is employed. Whether or not a long-chain branch exists in the propylene-based resin molecular chain can be confirmed by the following method. That is, extensional flow measuring device (for example, Rheometrics Inc. elongational flow measuring device: trade name RER-9000) using a measurement sample prepared from a propylene resin, strain rate (sec
^-1 ) is a graph showing the relationship between the extensional viscosity (poise) and the time (second). On this graph, the propylene resin having no propylene resin and long-chain branches having a long chain branching, such as propylene-based resin having a long chain branching Ri Na larger as the slope of the elongational viscosity curve time
In addition, while the elastic rupture eventually occurs , the slope of the elongational viscosity curve of the propylene-based resin having no long-chain branching decreases with time, which can be distinguished. The above rheometrics elongational flow measuring device (RER-9)
FIG. 5 is a graph showing the relationship between the elongational viscosity and the time at the strain rate of the propylene-based resin having long-chain branching and the propylene-based resin having no long-chain branching, from the measurement results according to 000). Curve A in the graph indicates a propylene-based resin having long-chain branches, and curve B indicates a propylene-based resin having no long-chain branches. From this graph, it can be seen that the slope of the elongational viscosity curve increases with time for the propylene-based resin having long-chain branches, whereas the slope of the elongational viscosity curve decreases with time for the propylene-based resin having no long-chain branches. I understand. The measurement sample and measurement conditions are as follows. Measurement sample size, shape: length 30 mm, diameter 5mm cylindrical-strain rate: 1.0 sec ^-1 Measuring temperature: melting point + 20 ° C. of the base resin (provided that the melting point of the base resin 1 The temperature at the top of the endothermic peak of the DSC curve obtained when 5 mg is heated at 10 ° C./min by a differential scanning calorimeter.)

The propylene resin as the base resin of the foamed sheet of the present invention has a drawdown property of 60 m / min or less, preferably 30 m / min or less, particularly preferably 15 m / min or less. The drawdown property means that a molten propylene resin heated to 230 ° C. is extruded into a string at a constant speed of 10 mm / min from a melt indexer nozzle (2.095 mm in diameter, 8 mm in length), and then to the string-like material. After passing through a feed roll located above a tension detection pulley located below the nozzle, the winding speed of the winding roll is gradually increased while winding by a winding roll. And the winding speed of the cord at the time of cutting.

The drawdown property can be adjusted by the number and length of the long-chain branches. Generally speaking, this value tends to decrease as the number of long-chain branches increases and the length of the branches increases. Therefore, in order to obtain a desired drawdown copolymer, it is necessary to set reaction conditions in consideration of these factors. In the case where the resin does not have long-chain branching, or has a branching that is too short or slight, or a normal propylene-based resin, the drawdown property exceeds 60 m / min. Extrusion foaming is performed using such a normal propylene-based resin to obtain a foamed sheet having a density of 0.3 to 0.06 g / cm ³ similar to the foamed sheet of the present invention. There are many corrugations and surface irregularities, and the product has no commercial value.

The propylene resin used in the present invention preferably has a half-crystallization time at the crystallization temperature + 15 ° C. of 800 seconds or more, and more preferably 1000 seconds or more. For the measurement of the half-crystallization time, a crystallization rate measuring device can be used.

In order to measure the half-crystallization rate, first, the support holding the film-like sample is put into an air bath of a crystallization rate measuring device to completely melt the sample, and then the molten sample is put together with the support. The sample is immersed in an oil bath maintained at the crystallization temperature of the sample + 15 ° C so as to block the optical path between the light source and the optical sensor, and is always kept at the optical sensor until the melted sample solidifies again. The voltage of the light source is adjusted so that the amount of light is detected, and a voltage-time curve as shown in FIG. 1 is obtained. In this case the voltage when the voltage at the curve becomes a constant value and the V _0, and the time until the voltage becomes 1 / 2V ₀ a half-crystallization time.

In the present invention, not only the above-mentioned propylene resin can be used alone, but also other resins can be mixed and used. As the resin used in combination, for example, a propylene-based resin other than the above, or high-density polyethylene, low-density polyethylene, linear low-density polyethylene,
Ethylene resins such as linear ultra-low density polyethylene, ethylene-butene copolymer, ethylene-maleic anhydride copolymer, butene resins, polyvinyl chloride, vinyl chloride such as vinyl chloride-vinyl acetate copolymer Resins, styrene resins and the like.

When the other resin is mixed, the amount of the resin to be mixed is limited to 40% by weight of the total weight of the polymer after mixing, and the drawdown property of the mixture does not exceed 60 m / min. There is a need.

The foamed sheet of the present invention has a density of 0.3 to 0.06.
g / cm ³ and a thickness of 1 to ³ mm. The density is 0.3g /
When it exceeds cm ³ , the heat insulating property is inferior, and when it is less than 0.06 g / cm ^{3, the} shape retention of the obtained molded article decreases. If the thickness of the sheet is less than 1 mm, the shape retention of the molded product is reduced,
If it exceeds 3 mm, molding becomes difficult.

In the present invention, the relationship of thickness of the skin layer / average thickness of the bubbles ≦ 2 is established between the skin layer formed on the foam sheet surface and the average thickness of the bubbles. The number of bubble films measured is defined as 2 to 15.

When heat molding is performed using a foamed sheet having a thick skin layer having a thickness ratio of more than 2, so-called pear tends to occur in a molded product. The most preferable thickness ratio is 0.5.
~ 1.5. When the number of the bubble films is less than 2,
When the foamed sheet is clamped at both ends and continuously transferred to form the sheet, both ends are easily broken, and the sheet cannot be transferred satisfactorily. If it exceeds 15, heating prior to molding must be performed for a long time due to its high heat insulating property, so that the molding cycle becomes longer and especially the heating of the surface becomes excessive, so-called surface burn occurs. It will be easier.

In the present invention, the average film thickness of the air bubbles is determined at random by using a microscope equipped with a scaler by cutting an arbitrary portion of the sheet in a direction perpendicular to the extrusion direction and using a microscope equipped with a scaler. It is an arithmetic mean value obtained by measuring points. The number of cell membranes in the thickness direction is the number of cell membranes arranged in the thickness direction of a cross section of the sheet cut in the same direction as above, excluding both skins. Therefore, the value of the number of bubbles in the thickness direction referred to in the present invention is a value obtained by subtracting 1 from the value of the number of bubbles measured in the thickness direction. In the present invention, the number of bubble films in the thickness direction needs to be 2 to 15 at an arbitrary portion of a cross section obtained by vertically cutting an arbitrary portion of the sheet.

In the foamed sheet of the present invention, a specific base resin is used, the density and the thickness are specified in specific ranges, and the surface skin layer has a thickness between the thickness of the surface skin layer and the average thickness of the bubbles. The respective requirements that the relationship of thickness / average film thickness of cells ≦ 2 is satisfied and the number of cell films in the thickness direction is defined as 2 to 15 are the heat insulating property of the foamed sheet (or a molded article using the same). The respective effects of shape retention, prevention of pear, and shortening of the molding cycle do not affect each other alone, and the above-mentioned excellent effects of the present invention are achieved only when the overall balance of each component is achieved. Is obtained. Further, the foamed sheet of the present invention, even when the base resin is a propylene homopolymer, has the above-mentioned specific constitutional requirements. Although it is better than a sheet that does not have the requirements, if the purpose of further deep drawing is intended, use a propylene-based copolymer as a base resin rather than using a propylene homopolymer as a base resin Is preferred.

As a method for obtaining the foamed sheet of the present invention, a method is employed in which a resin and a foaming agent are melt-kneaded in an extruder, and the melt-kneaded product is extruded under a low pressure through a die attached to the tip of the extruder to foam. Is done. In particular, in order to obtain a sheet-like foam, a method of using a circular die having an annular lip, extruding and foaming from the lip of the die to obtain a tube-like foam, and then cutting the tube to form a sheet. Is usually adopted.

The density and thickness of the obtained foamed sheet can be adjusted by adjusting the amount of the foaming agent and the lip gap of the die. Further, in order to satisfy the relationship of (thickness of surface skin layer / average thickness of bubbles ≦ 2) and to obtain a sheet having 2 to 15 bubbles in the thickness direction, a foaming agent is used in consideration of the physical properties of the resin used. This can be achieved by appropriately selecting the type and amount of the cell regulator, and by reducing the amount of blowing of a cooling medium such as air to the surface of the foam during foaming during extrusion.

In producing the foamed sheet of the present invention, as the foaming agent, an inorganic foaming agent, a volatile foaming agent, a decomposable foaming agent and the like can be used. Examples of the inorganic foaming agent include carbon dioxide, air, and nitrogen.

Examples of the volatile foaming agent include aliphatic hydrocarbons such as propane, n-butane, i-butane, pentane and hexane; cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane; trichlorofluoromethane; dichlorodifluoromethane. , Dichlorotetrafluoroethane, methyl chloride,
Halogenated hydrocarbons such as ethyl chloride and methylene chloride are exemplified.

Examples of the decomposition type foaming agent include azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and the like. These foaming agents can be appropriately mixed and used.

The amount of the foaming agent varies depending on the type of the foaming agent, the desired expansion ratio, and the like, but the density is 0.3 to 0.06 g.
The standard of the amount of the volatile foaming agent to be used to obtain a foam of / cm ³ is about 0.5 to 6 parts by weight (in terms of butane) per 100 parts by weight of the resin. Similarly, the amount is about 0.2 to 5 parts by weight (in terms of carbon dioxide) in the case of an inorganic foaming agent, and about 0.1 to 7.5 parts by weight in the case of a decomposable foaming agent.

In the present invention, a foam adjuster is added to the melt-kneaded product of the resin and the foaming agent, if necessary. Examples of the cell regulator include inorganic powders such as talc and silica, acidic salts of polycarboxylic acids, and reaction mixtures of polycarboxylic acids with sodium carbonate or sodium bicarbonate. It is preferable to add the foam control agent in an amount of about 13 parts by weight or less per 100 parts by weight of the resin (except when a large amount of the inorganic filler is contained in the resin). Further, if necessary, additives such as a heat stabilizer, an ultraviolet absorber, an antioxidant, and a colorant can be added.

In the present invention, the propylene-based resin or a mixture of the propylene-based resin and another resin may contain an inorganic filler up to 40% by weight of the total weight. Examples of the inorganic filler include talc, silica, calcium carbonate, clay, zeolite, alumina, barium sulfate and the like. Their average particle size is 1-70μ
m is preferable. When such an inorganic substance is contained in a large amount, the resulting foamed sheet has improved heat resistance and can reduce calorie burned during incineration.

The foamed sheet of the present invention can be formed by vacuum forming, pressure forming or the like as a foaming sheet which has been softened by heating, such as free drawing forming, plug and ridge forming, ridge forming, or the like. Matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming, plug assist forming, plug assist reverse draw forming, a method combining these, and the like can be applied. The foam sheet of the present invention is particularly suitable for forming containers for microwave ovens and lunch containers.

[0036]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. In Examples and Comparative Examples, the added amounts of the foaming agent and the cell regulator are% by weight when the total amount of these and the resin is 100% by weight. To measure the drawdown property and melt tension of the used resin, use a melt indexer,
Melt tension tester II manufactured by Toyo Seiki Seisaku-sho, Ltd.
The crystallization speed was measured using a crystallization rate measuring device MK-801 manufactured by Kotaki Shoji Co., Ltd. for the measurement of the half-crystallization time.

The properties of the resins used in the examples and comparative examples are as follows. Propylene resin A: Propylene / ethylene block copolymer having a long chain branch (“SD-
632 ": melting point 159.9 ° C., crystallization temperature 130.1 ° C., half-crystallization time 1353 seconds, MI = 2.0 g / 10 minutes, drawdown 3.1 m / min, melt tension 13.0 gf) Propylene Resin B: Propylene homopolymer having a long chain branch (“PF-814” manufactured by Himont, USA: melting point 1)
59.0 ° C, crystallization temperature 127.4 ° C, half-crystallization time 322
0 sec, MI = 2.2 g / 10 min, drawdown 3.5 m /
Min., Melt tension 17.4 gf) Propylene resin C: ordinary propylene / ethylene block copolymer having no long-chain branching (“J620G” manufactured by Nippon Petrochemical Co., Ltd .: melting point 162.4 ° C., crystallization temperature 113. 4
° C, semi-crystallization time 205 sec, MI = 1.8 g / 10 min, drawdown property 78.5 m / min or more, melt tension 1.6
gf)

Examples 1-4, Comparative Examples 1-4 A tandem extruder (first extruder: screw) containing a resin, a foaming agent (isobutane) and a foam regulator (monosodium citrate) in the proportions shown in Table 1 Diameter 65mm, L / D = 34,
Second extruder: compounded in a screw diameter of 90 mm, L / D = 32), melt-kneaded, and then attached to a tip of the extruder.
It is extruded and foamed into a tube from a circular die having a diameter of 0.3 mm (lip diameter) and a gap (lip clear) of 0.3 to 1.5 mm. On the inner and outer surfaces of the tubular foam, the temperature is shown in the column of "Blowing air temperature" in Table 1. Temperature air is blown, and the inner surface of the tubular foam is further cooled with a cooling mandrel (mandrel diameter 20).
0 mm), and the tubular foam was cut open in the extrusion direction to obtain a sheet. The extrusion conditions and the properties of the obtained foamed sheet (one week after production) are shown in Table 1.

[0039]

[Table 1]

(Forming A) Next, using the foamed sheets obtained in the above Examples and Comparative Examples, a forming test of the tray-like container shown in FIG. 2 was performed. The target tray-shaped container is a dish-shaped container having storage portions 2 and 3 on both sides of the partition 1 as shown in FIGS. 2 and 3. In FIGS. 2 and 3, each dimension of a to h is: a: 175 mm, b: 112 mm, c: 63 mm, d:
110 mm, e: 90 mm, f: 40 mm, g: 30 mm, h:
25 mm. In the molding test, each sheet was clamped at the approximate center of a heating furnace having a heater of 50 W at each of the upper and lower sides (distance between heaters: 20 cm), continuously guided, heated, and then continuously subjected to plug assist vacuum cleaning. Table 1 also shows the molding cycle (heating time per molding) in forming the tray-shaped container and the state of the obtained molded container.

(Forming B) A deep drawing test was performed using the same sheets as in the above Examples and Comparative Examples. The target molded product has a length: a = 453 mm as shown in FIG.
Width: 45 mm deep in foam sheet 4 with b = 300 mm
The hemispherical storage units 5 having a diameter of d = 80 mm are arranged in four rows horizontally, and the storage units 5 are arranged in five upper and lower rows so that the positions of the storage units 5 are shifted by half by the upper and lower rows. The aperture ratio of the storage section 3 is about 0.56. In the molding test, each sheet was clamped and guided to the approximate center of a heating furnace having a heater of 50 W on each side (distance between heaters: 20 cm), heated, and then continuously subjected to plug-assist vacuum molding. The molding cycle (heating time per molding) at the time of this molding and the state of the obtained deep-drawn molded product are also shown in Table 1.

The evaluations of the tray-shaped container forming test and the deep drawing container forming test were as follows: ・ ・ ・: Good molded product that does not meet the evaluations of (1) and (2) below. Δ: Molded product having a remarkably thin portion. ×: A molded product having a broken portion or / and a surface burn or / and a pear. And

[0043]

As described above, the foamed propylene-based resin sheet of the present invention has a long-chain branch and a draw-down property of not more than 60 m / min. With a density of 0.3 to 0.06
g / cm ³ , a thickness of 1 to ³ mm, and a relationship of thickness of the surface skin layer / average thickness of the bubbles ≦ 2 is established between the thickness of the surface skin layer and the average thickness of the bubbles. When the number of cell membranes is 2 to 15, the molding cycle of the foamed sheet based on the specific propylene-based resin can be shortened, and the occurrence of pears during molding can be prevented, and an excellent molded product can be obtained. it can.

Further, the density and the thickness are defined in specific ranges, a specific relationship between the thickness of the surface skin layer and the average thickness of the bubbles is established, and the number of the bubble films in the thickness direction is 2 to 15. The constituent elements act in a complex manner, and as a whole, an excellent effect is obtained in which the heat insulating property, the shape retaining property of the molded article, the moldability (easiness of molding, molding cycle, state of the molded article) are balanced.

Further, in the foamed sheet of the present invention, the density and thickness of the foamed sheet, the ratio of the thickness of the surface skin layer of the foamed sheet to the average cell thickness, and the number of cell membranes in the thickness direction are specified in specific ranges. Thus, even when a foamed sheet obtained by using a propylene homopolymer as a base resin is deep-drawn, effects such as superior moldability are obtained as compared to a foamed sheet in which these constituent requirements are not specified. Having.

[Brief description of the drawings]

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

FIG. 2 is a plan view of a tray-shaped container formed using the foamed sheets of Examples and Comparative Examples.

FIG. 3 is a side view of a tray-shaped container formed using the foamed sheets of the examples and comparative examples.

FIG. 4 is a plan view of a deep drawn product formed using the foam sheet of each of the examples and the comparative example.

FIG. 5 is a graph showing the relationship between elongational viscosity and time at the strain rate of a propylene-based resin having long-chain branches and a propylene-based resin having no long-chain branches.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C08L 23:10 (56) References JP-A-60-141728 (JP, A) JP-A-1-200931 (JP, A) Kaihei 5-32813 (JP, A) WO 91/13933 (WO, A1) (58) Fields investigated (Int. Cl. ⁶ , DB name) C08J 9/00-9/42 B29B 11/00-11 / 16 B29C 51/00-51/46 B29K 23:00 B29K 105: 04 C08L 23/00-23/36

Claims (1)

(57) [Claims] 1. A foamed sheet having a skin layer on the surface of a non-crosslinked propylene-based resin having a long chain branch and a drawdown property of 60 m / min or less, having a density of 0.3 to 0.3. 0.6 g / cm ³ , having a thickness of 1 to ³ mm, and satisfying the following relationship between the thickness of the surface skin layer and the average thickness of the bubbles: 2 bubbles in the thickness direction
15. A foamed propylene-based resin sheet, characterized in that it is 15.