Composite heat-insulating material containing a cellular urethane.

0001The present invention relates to a composite molded product which is useful for use, for example, an lining heat-insulating material of the main body or door of a refrigerator, a door material of a show window case or bath tub which is required to be heat-­insulating, a bumper of an automotive vehicle or an interior material for an automotive vehicle such as a door trimming, which require buffering properties, and a surfboard.

0002The door material of a bath tub has recently made of polyvinyl chloride sheet. However, when it is used at high temperature, the polyvinyl chloride sheet decomposes and generates chlorine gas, and an adjacent aluminum strip, e.g. of a shower enclosure, is corroded by the chlorine gas. In order to alleviate this problem, it has been proposed to arrange two polypropylene sheets on the aluminum sash to fill a space surrounded by the aluminum strip and the sheet, thereby providing rigidity to the door.

0003With respect to the interior material for an automotive vehichle such as the door trimming, it is known to fill with a foamed polyurethane by injection, to give good buffering properties and heat-insulating properties due to the replacement of a metal with a resin.

0004Thus, a composite of a shaped polymeric material and a cellulor foamed polyurethane is required to be produced in various complicated shapes.

0005However, the polymeric material is generally a sheet or a molded product obtained by heat molding or injection molding the sheet, and when a polyolefin having such shape is used, a void is formed due to insufficient adhesive strength between the polyolefin resin and the foamed polyurethane, and the rigidity and the heat-insulating properties cannot be sufficiently achieved.

0006Our prior EP-0150942A and US-4667097 discloses a heat-insulating material made by a process wherein a sheet of a polymer comprising at least 50 mol% of units of an olefin (e.g. a polyethylene) is coated on one surface with an aqueous solution or dispersion of an adhesive comprising 20 to 100 wt% of the solids of a polyolefin having carboxyl groups (e.g. a salt of an ethylene/acrylic acid copolymer). The adhesive may contain up to 80% of a N-containing water-soluble antistatic polymer and/or up to 2% of a F-containing surfactant.

0007The adhesive layer adheres strongly to a cellular foamed polyurethane, to form a composite heat-insulating material.

0008The polymer sheet can be deep-drawn to shape, adhesive-coated, placed over the metal pressing of a refrigerator body or door, and the urethane components injected through a hole in the sheet (see Fig 1) so that polyurethane is formed between the sheet and the metal pressing and is foamed and adhered<u style="single">in</u><u style="single">situ</u>.

0009We have now devised an improved adhesive for the aforesaid process and which is also useful in making other composite molded products.

0010The composite molded product according to the present invention has the structure that an olefin-­based resin molded product and a urethane foam are integrally laminated with an adhesive resin layer, the adhesive resin having a composition comprising by weight: <ul id="ul0001" list-style="none"><li>(A) 55 to 90% of a polymer comprising an olefin;</li><li>(B) 1 to 30% of a copolymer of ethylene and acrylic acid; and</li><li>(C) 10 to 30% of a polymer containing styrene-­units.</li></ul>

0011Examples of the olefin-based resin for forming the olefin-based resin molded product include a non-polar olefin-based resin such as a polyethylene, a polypropylene, an ethylene/propylene copolymer, an ethylene/propylene/butene copolymer, a polystyrene or a styrene/butadiene/styrene block copolymer, and a carboxyl group-containing olefin-based resin such as an ethylene/­acrylic acid random copolymer, an ethylene/methacrylic acid random copolymer, an acrylic acid-grafted poly­ethylene, a methacrylic acid-grafted polyethylene, a maleic anhydride-grafted polyethylene, a maleic anhydride-­grafted polypropylene, a maleic anhydride-grafted poly­propylene, a maleic anhydride-grafted ethylene/vinyl acetate copolymer, or an itaconic acid-grafted polyethy­lene. Those resins can be used alone or as mixtures thereof.

0012The olefinic-based resin can contain another polymer such as a polyamide, ABS or an ethylene/vinyl acetate copolymer, a stabilizer, a rubber, a pigment or an inorganic filler.

0013Further, the olefinic polymer can have a laminate structure, and a specific function can be imparted to the respective layer. For example, in the case where the olefin molded product constitutes a surface material of a show window case or an interior material of a refrigerator, a film made of a propylene homopolymer having a good luster is used as a surface layer, and a sheet made of the following composition having good vacuum forming properties is used as a substrate layer, the composition comprising <ul id="ul0002" list-style="none"><li>(a) 20 to 80% by weight, preferably 40 to 70% by weight, of a polypropylene;</li><li>(b) l0 to 80% by weight, preferably l0 to 55% by weight, of a polyethylene;</li><li>(c) 0 to 35% by weight, preferably 5 to 25% by weight, of a styrene-based resin, and</li><li>(d) 0 to 65% by weight, preferably 5 to 55% by weight,of an inorganic fine powder.</li></ul>

0014The polypropylene as Component (a) contributes to the adhesiveness to the propylene homopolymer of the surface luster layer. The polyethylene as Component (b) improves the deep drawing properties of a laminate sheet in vacuum forming. The styrene-based resin as Component (c) contributes to reduce sagging of a laminate sheet which is soften or molten by heating due to its own weight. The inorganic fine powder as Component (d) con­tributes to not only increase the rigidity of the olefin-­based resin molded product but also improve the cooling cycle during vacuum forming the laminate sheet.

0015Examples of the polypropylene as Component (a) include a propylene homopolymer, a random or black copolymer of propylene with an olefin such as ethylene, butene-l or hexene, 4-methylpentene-l, and a maleic anhydride-grafted polypropylene.

0016Examples of the polyethylene as Component (b) include a high density polyethylene, a low density polyethylene, an ethylene/vinyl acetate copolymer, a linear polyethylene, an ethylene/vinyl acetate copolymer, an ethylene/acrylic acid copolymer, an ethylene/meth­acrylic acid copolymer and SARLINE (a registered trade­mark, a product of du Pont).

0017Examples of the styrene-based resin include a polystyrene, a styrene/butadiene/styrene block copolymer (SBS), a styrene/acrylonitrile copolymer (SA), ABS and a high impact polystyrene (HIPS).

0018Examples of the inorganic fine powder as Component (d) include talc, calcium carbonate, diatomaceous earth, calcined clay and titanium oxide.

0019The adhesive resin composition which bonds the urethane foam and the olefin-based resin molded product is a mixture comprising (A) 55 to 90% by weight of the olefin-based resin, (B) l to 30% by weight of the ethy­lene/acrylic acid copolymer and (C) l0 to 30% by weight of the styrene-based resin. The mixture can additionally contain an ethylene/propylene copolymer rubber, a styrene/butadiene rubber or the like.

0020The same olefin-based resins as used in the substrate layer as described above, such as polypropylene or polyethylene, can be used as the olefin-based resin of Component (A). It is preferred to use the same type of the olefin-based resin as in the substrate layer. For instance, when the olefin-based resin of the substrate layer is a mixture of the propylene homopolymer and high density polyethylene, a propylene/ethylene random or block copolymer alone or a mixture of the propylene homopolymer and high density polyethylene is used as the olefin-based resin of the adhesive layer. The propylene/­ethylene block copolymer is preferably used. Use of this copolymer provides the advantage that the surface of the adhesive layer extruded from an extruder into a film-like state is coarser than the surface of the film-like adhe­sive layer obtained from the propylene homopolymer or the propylene/ethylene random copolymer, and so that the adhesive­ness between the urethane foam and the substrate layer is improved.

0021The ethylene/acrylic acid copolymer of Com­ponent (B) is a resin having a melt flow rate (MFR) of l to 400 g/l0 min measured at l90°C according to JIS K-6758. The resin is obtained by random copolymerization of 70 to 99% by weight of ethylene and 30 to l% by weight of acrylic acid. The resin is commercially available as YUKALON EAA A500W, YUKALON EAA A22lM and YUKALON EAA A200K, products of Mitsubishi Petrochemical Co., Ltd.

0022If the content of the ethylene/acrylic acid copolymer as Component (B) in the adhesive resin composi­tion is less than l% by weight, the adhesive strength between the urethane foam and the adhesive layer is poor. On the other hand, if the content thereof is larger than 30% by weight, the mold release property of sheet product when vacuum forming, press forming, pressure forming or injection molding the laminate sheet is poor. However, in the case of hollow molding, the face of the adhesive layer is inside the molded hollow product, and the problem on the mold release property can be disregarded.

0023In order to improve the mold release property, the styrene-based resin as Component (C) is added, and the amount of the ethylene/acrylic acid copolymer added is decreased. Examples of the styrene-based resin as Component (C) include a polystyrene, ABS, SBS, SA and HIPS. Those styrene-based resins can provide a high adhesiveness between the urethane foam and the adhesive layer.

0024The olefin-based resin alone as Component (C) in the adhesive does not have adhesive properties to the urethane foam.

0025The adhesive layer can be molded together with the olefin-based resin molded product. For example, each of resin compositions which form the luster layer, the substrate layer and the adhesive layer is melt kneaded using the individual extruder, the resulting three compositions are fed into one co-extrusion die, each layer is laminated in the die, and the resulting product is subjected to vacum molding, compression molding or blow molding to prepare a laminate for use as a lining material for a refrigerator, a surfboard or the like.

0026In the case of a molded product such as a bumper, the adhesive resin composition is injection molded into a metallic mold, the injection molded product is transferred into another metallic mold, and the polypropylene for a surface material is injection molded to obtain a laminate.

0027The thickness of the laminate is such that the thickness of the olefin-based resin molded product is 0.5 to 15mm, preferably 2 to 5mm, and the thickness of the adhesive layer is 5 to 100µ (for an extrusion molded product) or 0.5 to 2mm (an injection molded product).

0028If necessary and desired, the surface of the laminate is subjected to a corona discharge treatment or a plasma treatment.

0029Reference will now be made to the drawing, wherein: <ul id="ul0003" list-style="none"><li>Fig. 1 is a cross-section of apparatus and components being used to make part of a refrigerator incorporating material of the invention: and</li><li>Fig. 2 is a cross-section of an adhesive-coated sheet for use in the process of the invention, such as shown in Fig. 1.</li><li>Figure 2 is a cross-sectional view of the laminate 2, wherein 2c is a lustrous surface layer, 2a is the substrate and 2a is an adhesive layer.</li></ul>

0030The composite molded product is prepared by integrally bonding the olefin-based resin molded product and the urethane foam using the adhesive layer interposed therebetween.

0031A surfboard is prepared by pouring a foamable urethane solution into the hollow portion of the laminate prepared by blow molding, and foaming the urethane solution therein.

0032To produce the interior material of a refrigerator, a sheet of an olefinic polymer is coated, e.g. as shown in Fig. 2, with an adhesive , on the opposite surface to that which will be the visible face in the refrigerator lining.

0033This sheet 2 is then shaped, preferably by differen­tial pressure forming, to serve as a refrigerator lining, e.g. to have a recess 4 as shown in Fig. 1. The sheet is placed in a sheet metal (enamelled if not of stainless metal) refrigerator body or door 1, and an injection hole 6 is bored therein to receive the inlet 5 of injection apparatus 7, for the components 8 of an expandable urethane. The apparatus shown is for a "two-pack" urethane composition. The composition is injected into the cavity 3 between the metal frame 1 (serving here as a mould) and the polymer sheet 2, and is foamed to fill the cavity (as shown by stippling in Fig. 1) and to adhere to the underside of sheet 2.

0034The present invention is described in greater detail with reference to the following examples. All parts and percentages (%) are by weight. In the sheets, some polymers are referred to as "resins". ("MFR" means melt flow rate.)

Production of Sheet

SHEET PRODUCTION EXAMPLE 1

(i) Resin for Lustrous Layer (Surface Layer)

0035A crystalline propylene homopolymer (MFR: 2.0 g/10 min; boiling heptane extraction residue: 99% by weight) was used.

(ii) Resin for Deep Drawing Layer

0036mixture of 30% by weight of a crystalline propylene/­ethylene block copolymer (ethylene content: 5% by weight; MFR: g/10 min; boiling heptane extraction ´ ´ ´ residue: 98% by weight), 45% by weight of polyethylene (density: 0.950 g/cm³; MFR: 0.6 g/l0 min) and 20% by weight of talc having a particle diameter of l.5 µm was kneaded in an extruder and extruded in the form of strand. The strand was cut to form pellets.

(iii) Adhesive Resin on Urethane Foam Side.

0037A mixture of 85% by weight of a crystalline propylene/ethylene block copolymer having an ethylene content of 5% by weight, MFR of 0.5 g/l0 min and a boiling heptane extraction residue of 98% by weight, 5% by weight of an ethylene/acrylic acid random copolymer having an acrylic acid content of 20% by weight and MFR of 300 g/l0 min ("EAA 500W", a product of Mitsubishi Petrochemical Co., Ltd.), and l0% by weight of a polystyrene ("DIALEX HT5l6", a product of Mitsubishi Monsanto Chemical Co., Ltd.) was kneaded in an extruder and extruded in the form of a strand. The strand was cut to form pellets.

0038The above pellets of the resin (ii) were fed to a three-layer multimanifold die (width: 700 mm) at 230°C by means of an extruder (diameter of a screw: 90 mm), and the resin (i) and the adhesive resin compo­sition (iii) were fed each other to the same die as above at 220°C by means of two other extruders (diameter of a screw: 40 mm). The temperature of the die was set at 220°C. A molten three-layer sheet extruded from the die was cooled and solidified successively on three rolls having a width of 700 mm and then subjected to a corona discharge treat­ment to produce a laminate sheet for vacuum molding. The temperatures of the three rolls were as follows: 40°C for the nearest roll relative to the die; 95°C for the intermediate roll; and 40°C for the farthest roll. The rotation speed of the rolls was l.5 m/min. The total thickness of the sheet was l.6 mm; the thickness of the luster layer was 0.l5 mm; the thickness of the deep draw­ing layer (intermediate layer) was l.35 mm; and the thickness of the adhesive resin layer was 0.l mm.

SHEET PRODUCTION EXAMPLES 2 TO l0

0039Laminate sheets were prepared in the same manner as in Sheet Production Example l above except for chang­ing the composition of the adhesive resin layer as shown in the Table below.

0040The abbreviations in the Table are as follows. PP: A propylene/ethylene block copolymer E·AA: An ethylene/acrylic acid copolymer 500W: An ethylene/acrylic acid copolymer having an acrylic acid content of 20% by weight and MFR of 300 g/l0 min., a product of Mitsubishi Petrochemical Co. A22lM: An ethylene/acrylic acid copolymer having an acrylic acid content of 8.5% by weight and MFR of 7 g/l0 min., a product of Mitsubishi Petrochemical Co. PS: A polystyrene ("DIALEX HT5l6", a product of Mitsubishi Monsanto Chemical Co.) SBS: A styrene/butadiene/styrene block copolymer ("TUFFPRENE A", a product of Asahi Kasei Kogyo Co.)

EXAMPLE 1

0041The sheet obtained in Production Example 1 was introduced into an oven maintained at about 230°C and was subjected to plug assist vacuum molding (drawing ratio H/D/ = 1/1) using an air-pressure of 5.0 kg/cm² and a vacuum of -600 mm Hg by means of a vacuum/pressure molding machine. The mold release property of the sheet was good, and the plug was easily separated from the sheet.

0042An injection inlet was bored in the above-­molded sheet which was then placed in a stainless steel frame as the main body of a refrigerator. Into a cavity formed between the frame and the sheet was injected (as in Fig 1) through the injection inlet a two pack type expandable urethane solution, HM-l5l0, produced by Polyurethane Kagaku Kasei Co., Ltd. In l0 seconds after the injection of the urethane solution, it started to expand and in l minute the cavity was completely filled with a urethane foam. The density of the urethane foam was 0.05 g/cm³. This procedure was repeated 20 times to obtain 20 samples of the composite molded product.

0043After 24 hours,a test piece was cut out of the sheet with the urethane foam bonded thereto and was measured for the adhesion between the sheet and the urethane foam in the following method.

Adhesion Test:

0044After the urethane foam is peeled off from the test piece by hand, a cross cut test is conducted by making eleven parallel knife marks in one direction and eleven in the perpendicular direction in the residual adherent urethane to form l00 squares, and an adhesive tape is adhered thereto and rapidly peeled from the sheet to observe the percentage of the urethane unpeeled.

0045The results obtained are shown in the Table below.

0046The adhesion is evaluated in the following criteria. O: Cohesive failure of urethane foam Bonded portions of squares: 8l/l00 - l00/l00 Δ: Cohesive failure of urethane foam and inter­facial separation between adhesive and urethane simultaneously occur. Bonded portions of squares: 50/l00 - 80/l00, X: Adhesion between urethane foam and adhesive layer is poor, and the sheet is easily peeled off at the interface of urethane foam. Bonded portions of squares: 0/l00 - 49/l00

EXAMPLES 2 TO 5 AND COMPARATIVE EXAMPLES l TO 5

0047Composite molded products were obtained in the same manner as in Example l except that laminate sheets obtained in Sheet Production Examples 2 to 9 were used in place of the sheet obtained in Sheet Production Example l.

0048The adhesive between the urethane foam and the sheet in those composite molded products are shown in the Table below.

EXAMPLE 6

0049Using the mixture of 85% by weight of the pro­pylene/ethylene block copolymer, 5% by weight of the ethylene/acrylic acid copolymer "500W", and l0% by weight of the polystyrene, as the adhesive, and the homopoly­propylene as the surface layer, which were used in Example l, each was melt kneaded in the individual extruder at about 220°C, and those compositions were fed into one die and laminated therein. The laminated product was extruded in the form of a parison. The parison was blow-molded to obtain a molded product for surfboard.

0050The adhesion between the urethane foam and the adhesive layer in this product was stonger than that in the product of Example l.

EXAMPLE 7

(i) Resin for Luster Layer (Surface Layer)

0051A crystalline propylene homopolymer (MFR: 2.0 g/l0 min; boiling heptane extraction residue: 99% by weight) was used.

(ii) Resin for Deep Drawing Layer

0052A mixture of 40% by weight of a crystalline propylene/ethylene block copolymer (ethylene content: 5% by weight; MFR: 0.5 g/l0 min; boiling heptane extraction residue: 98% by weight), 40% by weight of polyethylene (density: 0.950 g/cm³; MFR: 0.6 g/l0 min) and 20% by weight of talc having a particle diameter of l.5 µ was kneaded in an extruder and extruded in the form of strand. The strand was cut to form pellets.

(iii) Adhesive Resin on Urethane Side

0053The same mixture was used in Example l.

0054The above pellets of the resin (ii) were fed to a three-layer multimanifold die (width: 700 mm) at 230°C by means of an extruder (diameter of a screw: 90 mm). The resin (i) was fed to the same die as above at 230°C by means of the separate extruder (diameter of a screw: 40 mm), and the adhesive resin (iii) was also fed to the same die as above at 220°C by means of other separate extruder. The temperature of the die was set at 230°C. A molten sheet extruded from the die was cooled and solidified successively on three rolls having a width of 700 mm and then subjected to a corona discharge treatment to produce a three-layer sheet for vacuum forming. The temperatures of the three rolls were as follows: 40°C for the nearest roll relative to the die; 95°C for the intermediate roll; and 50°C for the farthest roll. The rotation speed of the rolls was l.5 m/min. The total thickness of the sheet was l.6 mm; the thickness of the luster layer was 0.20 mm; the thickness of the deep drawing layer (intermediate layer) was l.25 mm; and the thickness of the adhesive layer was 0.l mm.

0055The sheet was subjected to the vacuum forming in the same manner as in Example l. The molded sheet was placed in a frame, and urethane foaming and molding were conducted to obtain a composite molded product.

0056The results obtained are shown in the Table below.

(i) Resin for Luster Layer (Surface Layer)

EXAMPLE 8

0057A crystalline propylene homopolymer (MFR: 2.0 g/l0 min; boiling heptane extraction residue: 99% by weight) was used.

(ii) Resin for Deep Drawing Layer

0058A mixture of 30% by weight of a crystalline propylene/ethylene block copolymer (ethylene content: 5% by weight; MFR: 0.5 g/l0 min; boiling heptane extraction residue: 98% by weight), 45% by weight of polyethylene (density: 0.950 g/cm³; MFR: 0.6 g/l0 min) and 20% by weight of talc having a particle diameter of l.5 µ was kneaded in an extruder and extruded in the form of strand. The strand was cut to form pellets.

(iii) Adhesive Resin on Urethane Side

0059A mixture of 65% by weight of a crystalline propylene/ethylene block copolymer (ethylene content: 5% by weight; MFR: 0.5 g/l0 min; boiling heptane extrac­tion residue: 98% by weight), l5% by weight of an ethylene/­acrylic acid having an acrylic acid content of 20% by weight and MFR of 300 g/l0 min ("500W", a product of Mitsubishi Petrochemical Co., Ltd.) and 20% by weight of acrylonitrile-­butadiene-styrene copolymer (ABS) was kneaded in an extruder and extruded in the form of a strand. The strand was cut to form pellets.

0060The above pellets of the resin (ii) were fed to a three-layer multimanifold die (width: 700 mm) at 230°C by means of an extruder (diameter of a screw: 90 mm), and the resin (i) and the adhesive resin compo­sition (iii) each was fed to the same die as above at 220°C by means of the separate extruders (diameter of a screw: 40 mm). The temperature of the die was set at 220°C. A molten sheet extruded from the die was cooled and solidified successively on three rolls having a width of 700 mm and then subjected to a 500 Watts corona discharge treatment to produce a laminate sheet for vacuum molding. The temperatures of the three rolls were as follows: 40°C for the nearest roll relative to the die; 95°C for the intermediate roll; and 50°C for the farthest roll. The rotation speed of the rolls was l.5 m/min. The total thickness of the sheet was l.6 mm; the thickness of the luster layer was 0.l5 mm; the thickness of the deep drawing layer (intermediate layer) was l.35 mm; and the thickness of the adhesive layer was 0.l mm.

0061The sheet was subjected to the vacuum molding. in the same manner as in Example l. The molded sheet was placed in a frame, and urethane foaming and molding were conducted to obtain a composite molded product.

0062The results obtained are shown in the Table below. <tables id="tabl0001" num="0001"><img file="EP0214747A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0214747A2_D0002.tif" /></tables>