JP5050911B2 - Laminated body for foaming and foam - Google Patents

Description

  The present invention relates to a laminate capable of obtaining a foam laminate having excellent heat insulation properties by heating and foaming and a foam obtained by heating and foaming the laminate, and particularly, there are very few irregularities on the surface of the foam. The present invention relates to a laminate capable of obtaining a foam laminate having excellent cosmetic properties, and a foam obtained by heating and foaming the laminate.

  Conventionally, a synthetic resin, in particular, a foamed polystyrene is often used as a container having heat insulation properties. However, the expanded polystyrene container has drawbacks such as high environmental load at the time of disposal and poor printability, and alternatives to other materials are being studied. Under such circumstances, a container in which corrugated paper is pasted on the outer peripheral surface of the paper cup body to form a heat insulating layer, a container in which a laminate of pulp nonwoven fabric and coated paper is bonded to the outer peripheral surface of the paper cup, etc. Has been developed and used.

  However, each method has a drawback that it is not easy to process and mold, and the cost is high. Therefore, a thermoplastic synthetic resin film having a low melting point is laminated and heated on at least one surface of the moisture-containing base material to foam the thermoplastic synthetic resin film using the moisture contained in the base material. A technique for forming a heat insulating layer has been devised (see, for example, Patent Documents 1 to 4).

  In Patent Document 1, polyethylene is extruded and laminated on at least one side of a paper having moisture, and the surface of the paper not laminated with polyethylene is heated on a laminated paper in which a layer that retains vapor pressure is formed by heating. A method of manufacturing a laminated paper having an irregular pattern on the surface is disclosed. Patent Document 2 discloses a heat-insulating paper container using such a laminated paper as a body member and a bottom plate member, and a manufacturing method thereof. However, the thermoplastic resin for the foam layer used in these laminates is not specified in terms of physical properties or properties other than low-density polyethylene, and is usually low-density polyethylene used for foam insulation containers. Then, it is difficult to obtain a foam having a beautiful appearance by foaming so that the thickness of the foam is uniform. As a phenomenon that often occurs, it seems that there is no conspicuous defect at a distance, but the foam thickness of the foam is not partially uniform, and if you look closely, there are many minute irregularities on the surface, as if ripples on the water surface There are cases where it looks as if it was standing. The cause of this is presumed that the resin itself constituting the foamed layer is in a non-uniform state, and it was difficult to improve by adjusting the foaming conditions and the moisture content of the base material.

  In Patent Document 3, a two-layer laminate film in which a high-melting point thermoplastic resin film is disposed outside a low-melting point thermoplastic resin film that is a foam layer is bonded to at least one side of paper, and the high-melting point is attached to the other side. A heat-insulating paper container having a good appearance produced by forming a container by adhering the thermoplastic carbon layer film and heat-treating the same and a method for producing the same are disclosed. According to this method, a heat-insulating paper container having a good appearance can be obtained, but in order to form a laminate film having a two-layer structure, processing with a tandem laminator or multilayer laminator, or double pasting with a single laminator. There is a problem that the processing method is restricted.

  In Patent Document 4, a specified printing ink having a composition blending with foaming is applied to the surface of a low-melting thermoplastic synthetic resin film that is a foam layer, and the temperature conditions and aging conditions at the time of heating and foaming the container are set. By specifying, a heat-insulating paper container having a smooth printed surface without unevenness and a method for producing the same are disclosed. However, the synchronization ink has an effect of not inhibiting the expansion of the foam layer of the printed portion, but does not have an effect of uniforming the foam itself, so it cannot improve the minute unevenness on the surface of the foam. In addition, since the fine irregularities on the surface of the foam are derived from the resin of the foam layer, there is a problem that it cannot be improved by specifying the conditions during heating and foaming.

  The material thus obtained can be suitably used for food packaging containers, for example, noodles and soup containers that can be cooked simply by pouring hot water. In these products, in recent years, the required level of cosmetics of containers has been increased from the viewpoint of product image, and there has been a strong demand for foams having a beautiful appearance with few irregularities.

Japanese Patent Publication No. 48-32283 JP-A-57-110439 JP-A-5-42929 JP 2001-270571 A

  The present invention has been made in view of the situation as described above, and exhibits excellent heat insulation by heating and foaming, and is a foam having a good surface appearance that hardly causes minute unevenness on the surface after foaming. The object is to provide a laminate obtained and a foam obtained by heating and foaming the laminate.

  As a result of intensive studies to solve the above problems, the present inventors can obtain an excellent foam appearance when a laminate using a high-pressure method low-density polyethylene having specific properties as a foam layer is foamed by heating. As a result, the present invention has been completed.

That is, according to the present invention, (a) in the molecular weight distribution curve measured by the GPC method, the ratio of components having a molecular weight of 100,000 or more to the whole is 30.0% or less, and (b) the number average measured by the GPC method The ratio Mw / Mn of the molecular weight (Mn) and the weight average molecular weight (Mw) is 8.5 or less. The layer is made of a high-pressure low-density polyethylene and the substrate layer contains water. Thus, the present invention relates to a laminate for heating and foaming, wherein the high-pressure low-density polyethylene layer becomes a foamed layer when foamed by heating. Further, the high-pressure low-density polyethylene has a melt mass flow rate measured in accordance with JIS K6922-1 (1997) in the range of 2 to 100 g / 10 min, and a density measured in accordance with JIS K6922-1 (1997). Relates to a laminate for heating and foaming in a range of 890 to 935 kg / m ³ . Furthermore, the present invention relates to a laminate for heating and foaming, wherein the lamination method is extrusion lamination. Furthermore, it is related with the foam obtained by heat-foaming the said laminated body.

  The present invention is described in detail below.

  The high-pressure method low-density polyethylene constituting the laminate of the present invention can be obtained by a conventionally known high-pressure radical polymerization method.

  Moreover, the high-pressure method low-density polyethylene constituting the laminate of the present invention has a molecular weight distribution curve measured by the GPC method shown below, and the ratio of components having a molecular weight of 100,000 or more to the whole is 30.0% or less. More preferably, it is 10.0 to 28.0% because the moldability is good and the appearance of the foam is good. When the ratio of the component having a molecular weight of 100,000 or more to the whole exceeds 30.0%, the foam thickness of the foam is partially uneven, and minute irregularities are generated on the surface, which is not preferable.

  A resin having a low ratio of high molecular weight components such as the high-pressure low-density polyethylene used in the present invention has not been used for foaming applications. As the foaming resin, it is common to use a resin having a high melt tension for the purpose of maintaining the shape of the bubbles during foaming. In high pressure low density polyethylene, it is known that the melt tension is related to the content of the high molecular weight component, and the higher the content ratio of the high molecular weight component, the higher the melt tension. Therefore, the resin used in conventional foaming applications has a high content of the high molecular weight component, and the effect obtained by using the high pressure method low density polyethylene with a low high molecular weight component ratio as in the present invention is It cannot be easily predicted.

  Further, the high-pressure method low-density polyethylene constituting the laminate of the present invention has a value of the ratio Mw / Mn of the number average molecular weight (Mn) and the weight average molecular weight (Mw) measured by GPC method is 8.5 or less. . More preferably, it is 3.0 to 8.0 because the moldability is good and the appearance of the foam is good. When the value of Mw / Mn exceeds 8.5, the foam thickness of the foam becomes partially uneven, and minute irregularities are generated on the surface, which is not preferable.

  Here, the measurement method of the molecular weight distribution curve, number average molecular weight (Mn) and weight average molecular weight (Mw) by the GPC method defining the present invention will be described below.

  After weighing the high-pressure low-density polyethylene to be measured, BHT (manufactured by Wako Pure Chemical Industries, Ltd.) as an antioxidant is added to HPLC grade 1,2,4-trichlorobenzene (manufactured by Wako Pure Chemical Industries, Ltd.). The sample solution was dissolved by shaking at 140 ° C. for 1 hour in addition to 0.1% added solvent.

  Using Tosoh Co., Ltd. HLC-8121GPC / HT as a measuring device, it measured as follows. Three TSKgelGMHHR-H (20) HT (manufactured by Tosoh Corporation, inner diameter 7.8 mm, length 30 cm) were connected and used as a separation column. For the moving layer, HPLC grade 1,2,4-trichlorobenzene (Wako Pure Chemical Industries, Ltd.) with 0.05% BHT (Wako Pure Chemical Industries, Ltd.) added as an antioxidant is used. And moved through a separation column maintained at 140 ° C. at a flow rate of 1.0 mL / min. 0.3 mL of a sample solution whose concentration was adjusted to 1.0 mg / mL was injected into this, and sample components separated by a differential refractometer were detected. A molecular weight distribution curve, a number average molecular weight (Mn), and a weight average molecular weight (Mw) were calculated using a quintic approximation curve prepared using standard polystyrene (manufactured by Tosoh Corporation) as a calibration curve.

  The high-pressure process low-density polyethylene constituting the laminate of the present invention has a MFR of 2 to 100 g / 10 minutes, preferably 3 to 50 g / 10 minutes, more preferably 3 to 25 g / 10 minutes. It is preferable because of its excellent foamability and easy molding.

Further, the high-pressure method low-density polyethylene constituting the laminate of the present invention has a density of 890 to 935 kg / m ³ , preferably 900 to 925 kg / m ³ , more preferably 905 to 925 kg / m ³ . In addition to being excellent in the foamability of the laminate, when the laminate is heated and foamed, the amount of heat required for heating for foaming can be reduced, which is preferable.

  The physical properties other than the molecular weight distribution of the high-pressure method low-density polyethylene constituting the laminate of the present invention are not particularly limited, but the melt tension at 130 ° C. measured with a capillary viscometer is in the range of 80 to 300 mN. In order to obtain a foam having a good appearance, it is preferable. When the melt tension is less than 80 mN, when the laminate is heated and foamed, the foamed cells are bonded and broken, and the foamed cells shrink during cooling, resulting in many large irregularities on the foamed surface and worsening the surface appearance. There is a fear. On the other hand, when the melt tension exceeds 300 mN, there is a possibility that a sufficient thickness of the foamed layer cannot be obtained when the laminate is heated and foamed. In addition, the measuring method of melt tension is described below.

  In a thermostatic chamber set at 23 ° C., a capillary viscometer with a barrel diameter of 9.55 mm was equipped with a die having a length of 8 mm, a diameter of 2.095 mm, and an inflow angle of 90 °. The temperature was set to 130 ° C., the piston lowering speed was set to 10 mm / min, the stretch ratio was set to 24, and the load (mN) required for take-up was taken as the melt tension. When the maximum draw ratio was less than 24, the load (mN) required for taking up at the highest draw ratio that did not break was taken as the melt tension.

  The high pressure low density polyethylene constituting the laminate of the present invention may be mixed with one or more other polyethylene resins. There are no particular restrictions on the molecular weight distribution curve and the value of Mw / Mn after the high pressure method low density polyethylene and other polyethylene resins are melt mixed. However, when the polyethylene resin is high pressure method low density polyethylene, the molecular weight distribution curve and Mw / Mn value after melt-mixing these must satisfy the requirements of the high pressure method low density polyethylene of the present invention. I must.

  Examples of the polyethylene resin include low density polyethylene produced by a conventionally known high pressure radical polymerization method, ethylene / α-olefin copolymer produced using a Ziegler-Natta catalyst or metallocene catalyst, and high density polyethylene. be able to. The α-olefin constituting the ethylene / α-olefin copolymer is propylene, 1-butene, 4-methyl-1-pentene, 3-methyl-1-butene, 1-pentene, 1-hexene, 1 -Heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene and the like can be exemplified.

  Although there is no restriction | limiting in particular about a mixing ratio, Since favorable foamability and workability are obtained, it is preferable that the ratio of the polyethylene-type resin to mix is less than 50%, More preferably, it is less than 30%.

  The mixing method is not particularly limited, and may be a pellet mixture obtained by mixing pellets in a solid state, but the mixture melt-kneaded by a single screw extruder, a twin screw extruder, a kneader, a Banbury, etc. This is preferable because a product with stable quality can be obtained. When using a melt-kneading apparatus, the melting temperature is preferably about the melting point of polyethylene resin to about 300 ° C.

  The high-pressure low-density polyethylene constituting the laminate of the present invention is generally used for polyolefin resins such as antioxidants, light stabilizers, antistatic agents, lubricants, antiblocking agents, etc., as necessary. Additives may be added as long as the object of the present invention is not impaired.

  Commercially available products that can be used as the high-pressure method low-density polyethylene constituting the present invention include petrocene 204, petrocene 205, petrocene 207, petrocene 208, petrocene 209, petrocene 214, petrocene 217, petrocene 222, petrocene 225, and petrocene 226. And Petrocene 310 (both manufactured by Tosoh Corporation) and the like.

There is no particular limitation on the base material constituting the laminate of the present invention, moisture contained in the substrate is preferably 20 to 30 g / ^{m 2,} more preferably from 20~28g / ^{m 2.} If it is less than 20 g / m ² , the thickness of the foamed layer when the laminate is foamed may be insufficient. On the other hand, if it exceeds 30 g / m ² , when the laminate is heated and foamed, the foamed cells are bonded and broken, and the foamed cells shrink during cooling, resulting in many large irregularities on the foamed surface, resulting in a surface appearance. There is a risk of worsening.

As the base material constituting the laminate of the present invention, paper made of natural pulp such as high-quality paper and kraft paper (hereinafter simply referred to as paper), synthetic fiber or synthetic resin film is made pseudo-paper. So-called synthetic paper, foamed sheets, sheets made of porous inorganic materials such as zeolite, and the like can be exemplified, and paper is preferable because it is relatively easy to adjust the amount of water contained in the substrate. The substrate may be printed with colored ink or the like by a conventionally known technique. When using paper substrate, since the easy adjustment of water content, the basis weight is preferably 150~500g / ^{m 2,} more preferably from 200 to 400 g / ^{m 2.}

  Examples of the method for forming the laminate of the present invention include an extrusion laminate forming method, a dry laminate forming method, a wet laminate forming method, a thermal laminate forming method, a hot melt laminate forming method, and a compression forming method. Among these, the extrusion laminate molding method is preferable from the viewpoints of production efficiency and the quality of the molded laminate. Examples of the extrusion laminating method include various laminating methods such as a single laminating method, a tandem laminating method, a sandwich laminating method, and a coextrusion laminating method. The temperature of the resin in the extrusion laminating method is preferably in the range of 260 to 350 ° C, and the surface temperature of the cooling roll is preferably in the range of 10 to 50 ° C.

Further, in the extrusion laminating process, immediately after the high-pressure method low-density polyethylene is made into an extruded layer in a molten state, the base material adhesion surface of the layer is exposed to an oxygen-containing gas or an ozone-containing gas, and a method of bonding to the base material is used. From the viewpoint of excellent adhesion to the substrate layer. When the adhesiveness between the thermoplastic resin and the substrate is improved by the ozone-containing gas, the ozone gas treatment amount is 0.5 mg or more of ozone per 1 m ^{2 of the} film made of the thermoplastic resin extruded from the die. It is preferable to spray.

  In order to further improve the adhesion between the high-pressure method low-density polyethylene layer and the base material layer, the laminate of the present invention has a temperature at which the high-pressure method low-density polyethylene does not foam, for example, 30 ° C. to 60 ° C. for 10 hours. The heat treatment can be performed as described above. Moreover, you may perform well-known surface treatments, such as a corona treatment, a flame treatment, and a plasma treatment, with respect to the adhesive surface of a base material as needed. If necessary, an anchor coating agent may be applied to the substrate.

  In the laminate of the present invention, the thickness of the high-pressure method low-density polyethylene layer that foams by heating is not particularly limited as long as the object of the present invention is achieved, but is excellent in foamability and has few problems such as breakage. The thickness is preferably 30 μm to 5 mm, and the range of 30 μm to 150 μm is most preferable from the viewpoint of economy.

  When the laminate of the present invention is foamed by heating, it is preferable that the thickness of the foamed layer after foaming is 500 μm or more because the heat insulation of the foam laminate is excellent.

  In the laminate of the present invention, when the back side of the base material layer with respect to the high-pressure method low-density polyethylene layer foamed by heating is covered with a polymer film and sheet, an adhesive tape, etc., the water content of the base material layer is high. It is preferable because it can be prevented from being diffused from the back side of the low-density polyethylene layer and can be effectively foamed. These polymer films and sheets may be those deposited by aluminum vapor deposition, alumina vapor deposition, or silicon dioxide vapor deposition. Further, these polymer films and sheets may be further printed using urethane ink or the like. As a coating method, in addition to a lamination method such as extrusion lamination, dry lamination, and wet lamination, and a pressure bonding method, only an adhesive tape may be attached. Among them, since it is easy to prevent moisture from being removed from the laminate during heating and foaming, it is easy to prevent foaming. Therefore, a polymer polymer having a higher density than the high-pressure low-density polyethylene used as the foam layer is laminated. It is particularly preferred. The polymer is preferably a mixture of high-density polyethylene and high-pressure low-density polyethylene because laminate molding is relatively easy and the melting point can be easily adjusted. When the mixing ratio of the high-density polyethylene and the high-pressure low-density polyethylene is 15/85 to 85/15 by weight, laminate molding is relatively easy, and moisture is removed by foaming by melting during heating and foaming. This is preferable because it is easy to prevent obstruction.

  The laminate of the present invention can be foamed by heating in an oven or the like to obtain a foam having sufficient heat insulation. As a heating method, in addition to hot air, electric heat, and electron beam, any means such as forming a laminate into a container shape, filling a high-temperature object and utilizing the heat of the filling can be used. Heating can be performed by a batch method in an oven, a continuous method using a conveyor, or the like.

  The heating temperature and the heating time for foaming vary depending on the substrate used and the type of thermoplastic resin, but generally the heating temperature is 110 ° C. to 200 ° C., and the heating time is 10 seconds to 5 minutes.

  The foam of the present invention is suitably used for containers that are required to have heat insulation properties, such as paper containers for high-temperature beverages such as coffee and soup, and containers for instant foods such as instant noodles, and that require cosmetic appearance of products. can do.

  The laminate of the present invention is easily foamed by heating, exhibits excellent heat insulation properties, hardly causes micro unevenness due to a slight difference in foam thickness, has a good appearance on the surface after foaming, and is cosmetic. A very excellent foamed laminate can be obtained.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

  Below, the evaluation method of each physical property is shown.

(1) Moisture content of substrate Measurement was performed using a Karl Fischer method moisture measurement device (trade name CA-05, manufactured by Mitsubishi Chemical Corporation) at a measurement temperature of 165 ° C.

(2) Melt mass flow rate (MFR)
Measured according to JIS K6922-1 (1997).

(3) Density The density was measured according to JIS K6922-1 (1997).

(4) Measurement of molecular weight distribution curve by GPC method, number average molecular weight (Mn) and weight average molecular weight (Mw) According to the method described in the detailed description of the present invention, molecular weight distribution curve of high-pressure method low density polyethylene, number average molecular weight And the weight average molecular weight was measured. From the molecular weight distribution curve obtained by this method, the ratio of the components having a molecular weight of 100,000 or more to the whole was calculated, and Mw / Mn was calculated from the values of the number average molecular weight and the weight average molecular weight.

(5) Melt tension A capillary viscometer (Toyo Seiki Seisakusho, trade name: Capillograph) having a barrel diameter of 9.55 mm was equipped with a die having a length of 8 mm, a diameter of 2.095 mm, and an inflow angle of 90 °. The temperature was set to 130 ° C., the piston lowering speed was set to 10 mm / min, the stretch ratio was set to 24, and the load (mN) required for take-up was taken as the melt tension. When the maximum draw ratio was less than 24, the load (mN) required for taking up at the highest draw ratio that did not break was taken as the melt tension. The measurement was performed in a constant temperature room set at 23 ° C.

(6) Thickness of foam layer The laminates obtained in the examples were cut into 20 cm × 30 cm, allowed to stand for 210 seconds in a small oven (made by Werner Mathis AG) heated to 115 ° C., and then taken out and room temperature in air. Until cooled. Samples of the laminate after foaming and the laminate laminate before foaming as a blank were taken, and cross-sectional photographs were taken with an optical microscope. The thickness of the foam layer was measured from the cross-sectional photograph, and the average thickness of the foam layer measured at five locations was taken as the foam layer thickness of the foam.

(7) State of foamed surface The laminate obtained in the example was cut into 20 cm × 30 cm, left standing in a small oven (made by Werner Mathis AG) heated to 120 ° C. for 120 seconds, and then taken out at room temperature in the air. Until cooled. Light from a fluorescent lamp was applied to the surface of the obtained foam from an angle of 45 ° with respect to the surface, and the degree of shadow that appeared on the surface due to irregularities on the surface of the foam was visually observed. The case where the shadow was clearly identifiable was indicated as x, and the case where the shadow was hardly confirmed was indicated as ◯.

Example 1
The MFR is 8 g / 10 min, the density is 920 kg / m ³ , the Mw / Mn value measured by the GPC method is 7.9, and the ratio of components having a molecular weight of 100,000 or more to the whole is 26.3%. A high-pressure low-density polyethylene (trade name Petrocene 214 manufactured by Tosoh Corporation) (A1) having a melt tension at 130 ° C. of 160 mN measured with a capillary viscometer was converted into a single-screw extrusion laminator (Musashinokikai ( Co., Ltd.), extruded from a T-die at a temperature of 310 ° C., a moisture content of 24 g / m ² , a grammage of 320 g / m ² and a take-up speed of 60 m / min, an air gap Extrusion lamination was performed so that the passage time was 0.12 seconds and a thickness of 70 μm. Furthermore, a thermoplastic resin (trade name Petrocene LW04-1 manufactured by Tosoh Corporation) having a density of 940 kg / m ³ is formed to a thickness of 40 μm on the back side of the base material layer with respect to the polyethylene-based resin layer of this laminate. Extrusion lamination was performed to obtain a laminate in which a high-pressure method low-density polyethylene resin layer, a paper base material layer, and a thermoplastic resin layer were laminated in this order. This laminated body was heated and foamed, and the state of the foam surface was evaluated. The results of foamability evaluation are shown in Table 1. The state of the foam surface after foaming was very good.

Example 2
As a high-pressure method low density polyethylene, the MFR is 7 g / 10 min, the density is 922 kg / m ³ , the Mw / Mn value measured by the GPC method is 8.4, and the ratio of components having a molecular weight of 100,000 or more to the whole Example 1 except that high-pressure low-density polyethylene (trade name Petrocene 204 manufactured by Tosoh Corporation) (A2) having a melt tension of 170 mN at 130 ° C. measured by a capillary viscometer was 26.4%. Extrusion lamination was performed in the same manner as described above to obtain a laminate. This laminated body was heated and foamed, and the state of the foam surface was evaluated. The results are shown in Table 1. The state of the foam surface after foaming was very good.

Example 3
The high-pressure method low-density polyethylene has an MFR of 3 g / 10 min, a density of 924 kg / m ³ , a Mw / Mn value measured by the GPC method of 6.3, and a ratio of components having a molecular weight of 100,000 or more to the whole. Example 1 except that high pressure method low density polyethylene (trade name Petrocene 205 manufactured by Tosoh Corporation) (A3) having a melt tension of 230 mN at 130 ° C. measured by a capillary viscometer was 26.6%. Extrusion lamination was performed in the same manner as described above to obtain a laminate. This laminated body was heated and foamed, and the state of the foam surface was evaluated. The results are shown in Table 1. The state of the foam surface after foaming was very good.

Example 4
(A1) is blended with 20% by weight of an ethylene / 1-hexene copolymer (trade name Nipolon Z 04P67D manufactured by Tosoh Corporation) having an MFR of 13 g / 10 min and a density of 905 kg / m ³ , and 50 mm single screw extrusion. Extrusion laminate molding was carried out in the same manner as in Example 1 except that a granulated product after melt-kneading at 150 ° C. by a machine (Placo Co., Ltd.) was used as the high-pressure method low-density polyethylene to obtain a laminate. The granulated resin had a Mw / Mn value of 6.5 measured by the GPC method, a ratio of 23.8% of the total components having a molecular weight of 100,000 or more, and was measured with a capillary viscometer. The melt tension at 130 ° C. was 130 mN. This laminated body was heated and foamed, and the state of the foam surface was evaluated. The results are shown in Table 1. The state of the foam surface after foaming was very good.

Comparative Example 1
As a high-pressure method low density polyethylene, the MFR is 8 g / 10 min, the density is 918 kg / m ³ , the Mw / Mn value measured by the GPC method is 9.7, and the ratio of the components having a molecular weight of 100,000 or more to the whole Example 1 except that high-pressure low-density polyethylene (trade name Petrocene 213 manufactured by Tosoh Corporation) (A4) having a melt tension of 180 mN at 130 ° C. measured by a capillary viscometer was 30.6%. Extrusion lamination was performed in the same manner as described above to obtain a laminate. This laminated body was heated and foamed, and the state of the foam surface was evaluated. The results of foamability evaluation are shown in Table 1. The state of the surface of the foam was unsatisfactory with many minute irregularities.

Comparative Example 2
The high-pressure method low-density polyethylene has an MFR of 13 g / 10 min, a density of 919 kg / m ³ , a Mw / Mn value measured by the GPC method of 8.7, and a ratio of the components having a molecular weight of 100,000 or more to the whole. Example 1 except that high pressure method low density polyethylene (trade name Petrocene 212 manufactured by Tosoh Corporation) (A5) having a melt tension of 100 mN at 130 ° C. measured by a capillary viscometer was 28.7%. Extrusion lamination was performed in the same manner as described above to obtain a laminate. This laminated body was heated and foamed, and the state of the foam surface was evaluated. The results of foamability evaluation are shown in Table 1. The state of the surface of the foam was unsatisfactory with many minute irregularities.

Claims (4)

It consists of at least two layers of a high pressure method low density polyethylene layer that satisfies the following requirements (a) to (b) and a base material layer containing ²⁰ to 30 g / m ² of water, and the high pressure method low density when foamed by heating. A laminate for heating and foaming, wherein the polyethylene layer is a foamed layer.
(A) In the molecular weight distribution curve measured by the GPC method, the ratio of components having a molecular weight of 100,000 or more to the whole is 30.0% or less. (B) The number average molecular weight (Mn) and the weight average molecular weight measured by the GPC method ( Mw) ratio Mw / Mn is 8.5 or less The laminate for heating and foaming according to claim 1, wherein the high-pressure method low-density polyethylene layer satisfies the following requirements (c) to (d).
(C) The melt mass flow rate measured by JIS K6922-1 (1997) is 2 to 100 g / 10 min. (D) The density measured by JIS K6922-1 (1997) is 890 to 935 kg / m ^3. The laminate for heating and foaming according to claim 1 or 2, wherein the lamination method of the high-pressure method low-density polyethylene layer and the base material layer is extrusion lamination. The foam obtained by heat-foaming the laminated body for heat foaming in any one of Claims 1-3.