JP2008068529A - Manufacturing method for polypropylene-based laminated and foamed sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a polypropylene-based resin laminated foamed sheet for forming a container with a stably peelable surface film, which makes the polypropylene-based resin laminated foamed sheet stably, continuously and economically manufactured by using printing ink originally used for designedness. <P>SOLUTION: In the polypropylene-based resin laminated foamed sheet, a polypropylene-based resin film, which is printed on a polypropylene-based resin foamed sheet, is superposed in such a manner that a printing surface is directed to an inside (the side of the foamed sheet). Characteristically, the polypropylene-based laminated foamed sheet is extrusion-laminated by using a polypropylene-based resin so that the peel strength of the polypropylene-based resin film and the printing ink bonded to the polypropylene-based resin foamed sheet can be set to be in the range of 0.3-1.5 N/15 mm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a polypropylene resin laminated foam sheet for forming a polypropylene container from which a film on the surface can be peeled.

  Polypropylene foam containers formed by molding polypropylene resin laminate sheets are excellent in heat resistance, heat insulation, oil resistance, and the like, and are currently used as food containers for reheating in microwave ovens such as convenience stores.

  On the other hand, it is important to collect and reuse these molded articles after use from the viewpoint of waste disposal and resource saving. However, since these containers are filled with food that has been heated to a high temperature by reheating, the inner surface in contact with the food is dirty and cannot be reused as it is.

As one of these recovery methods, it is considered that a film is stuck instead of cleaning the inner surface of the molded product, and after use, the film is peeled off, and only the molded product main body is recovered and recycled. Further, as a method for laminating these films, it has been proposed to laminate a film coated with a co-pressing method or an adhesive by a heat laminating method. However, it is expensive because it is laminated by a special method. Moreover, it was difficult to obtain a stable peel strength. That is, if the peel strength is too strong, the film or substrate may be broken or not peeled at all during peeling. In addition, those with too weak peel strength were poor in practicality, such as peeling off the film during molding or use.
Patent 3028101 Patent 3020079

  The present invention is a method for producing a polypropylene resin laminated foam sheet for forming a container capable of stably peeling a surface film without using a special adhesive, and is a printing method originally used for design The objective is to produce ink stably and continuously and economically.

  That is, the gist of the present invention is a polypropylene resin laminated foam sheet in which a printed polypropylene resin film is laminated on a polypropylene resin foam sheet on the inside (foam sheet side), and the polypropylene resin foam sheet side. A method for producing a polypropylene-based laminated foamed sheet characterized by laminating by extrusion lamination with a polypropylene-based resin so that the peel strength between the printed layer and the polypropylene-based resin film bonded to each other is 0.3 to 1.5 N / 15 mm More preferably, the printing layer is made of an ink based on a resin made of chlorinated polypropylene, chlorinated EVA or a mixture.

Moreover, it is more preferable that the application amount of printing ink is 1 to 7 g / m ² .

  According to the present invention, a container capable of easily peeling off a film from the surface of the container can be stably produced at a low cost. That is, in the state where the container filled with food is cooked and eaten, the inner surface of the container is contaminated, but this contamination can be easily removed together with the film, and special treatment is performed. In addition, a container that is easy to recycle and can be provided at low cost.

  The present invention will be described in detail below.

  The polypropylene-based resin film used in the present invention is a film mainly composed of a polypropylene-based resin such as a polypropylene homopolymer or a polypropylene copolymer, and is commonly used so-called CPP or OPP, that is, unstretched or biaxially stretched. It can be used regardless of the film forming method. Moreover, you may use not only a single layer but the multilayer film of two or more layers.

  The printing layer in the present invention is formed by printing by a gravure printing method using an ink mainly composed of a mixture of a resin / pigment and a solvent. So-called water-based inks that are more environmentally friendly from the current trend may be used. Resins for printing inks include copolymers of vinyl chloride and vinyl acetate, chlorinated products of rubber, chlorinated products of EVA, chlorinated products of polypropylene, polymers of acrylic acid and its derivatives, condensates of dimer acid and polyamine, acrylic Examples thereof include polymers of acids and derivatives thereof, polymers of polyesters or polyethers and diisocyanates, and nitrate esters of cellulose. Moreover, you may use those resin 1 type or in mixture of 2 or more types. In particular, from the viewpoint of adhesiveness with a polypropylene resin, chlorinated polypropylene, chlorinated EVA, or a mixture thereof is preferable.

  In the gravure printing method, after the ink is applied to the surface, the solvent is dried and removed, and generally the adhesive strength of the printed film is not so strong. In order to make it stronger, it is generally used that a reaction ink such as isocyanate is used, or that it is further cured with an adhesive layer such as a dry laminating method. In the present invention, the fact that the adhesive strength of ink is stable and weak is utilized.

  The printing pattern in the present invention is not particularly limited, but in order to stabilize the peel strength, the area occupied by the printing layer in the printing film is preferably 50% or more. The area occupied by the film is preferably 100%.

The coating amount of the printing ink is preferably from 1 to 7 g / m ^2, more preferably 2-5 g / m ^2. If it is 7 g / m ² or more, the peel strength may be too weak, and peeling at the time of molding may occur. Moreover, if it is less than 1 g / m < ² > or there is no printing layer, peeling strength will become too strong and the target film peeling will not be achieved.

  In the printing ink, since the resin component that disperses the printing ink adjusts the adhesion to the film, if the pigment ratio in the printing ink is less than 10%, the printing ink is in the same state as a so-called anchor coat, The peel strength is more than necessary. In general, the anchor coat is a coating of the resin itself excluding the printing ink that hinders the adhesiveness in order to increase the adhesive strength between the printing ink and the printing film. On the contrary, if the pigment ratio is 30% or more, the peel strength becomes too weak and peeling occurs at the stage of molding or the like, which is not practical. That is, the pigment ratio is preferably 10% or more and less than 30%.

  The amount of printing ink applied is that after the printing layer is formed and the solvent is removed by drying. The coating amount can be achieved by adjusting the plate depth in gravure and adjusting the dilution amount of the ink with a solvent or water.

  In the present invention, the polypropylene film provided with the print layer and a polypropylene foam sheet described later are laminated with a polypropylene resin by an extrusion laminating method. Examples of the polypropylene resin for lamination include homopolypropylene, polypropylene-ethylene random copolymer, and polypropylene-ethylene block copolymer.

  In the extrusion laminating method, a molten polypropylene resin is extruded from a T-shaped die, and the polypropylene resin itself melted at 200 to 250 ° C. is used as an adhesive layer. The polypropylene resin is perpendicular to the flow direction of the polypropylene resin foam sheet as a base material. This is a known technique in which a polypropylene resin that is sanded with a polypropylene film is thermocompression bonded in a molten state so that the adhesive surface becomes a printing surface. The thickness of the polypropylene resin is preferably 30 μm to 120 μm. If the thickness of the polypropylene resin is 30 μm or less, there is a possibility that the peel strength of the obtained laminated foamed sheet is not sufficient, and if it is 120 μm or more, the cost is excessively undesirable. The peel strength between the film and the polypropylene foam sheet is defined by the weakness of the adhesive strength between the printing ink and film, the peel strength between the printing ink and the polypropylene resin, or the peel strength between the polypropylene resin and the polypropylene foam resin sheet. However, the peel strength of the ink-polypropylene resin and the peel strength of the polypropylene resin and the polypropylene foamed resin sheet are usually 1.5 N / 15 mm or more, and the adhesive strength between the printing ink and the film is the actual peel strength. . This peel strength can be adjusted by the printing conditions such as the pigment ratio in the printing ink, the coating amount of the printing ink, and the drying temperature, as well as the lamination conditions such as the resin temperature during bonding and the bonding pressure.

  In addition to additives such as anti-fogging agents, anti-blocking agents, lubricants, fillers, etc., polypropylene-based master batches based on polypropylene or polyethylene with pigments added to increase design can be added to polypropylene resins. Also good. In particular, since the pigment concentration and the coating amount in the printing ink are limited, it is preferable to color the polypropylene resin layer within a range that does not affect the peelability from the viewpoint of design.

  Long chain branching is introduced by irradiating an electron beam to a polypropylene resin (hereinafter referred to as a “raw polypropylene resin”) as a base resin used in the production of a polypropylene foam sheet in the present invention. A modified polypropylene resin obtained by melting and kneading a raw material polypropylene resin, an isoprene monomer, and a radical polymerization initiator (for example, HMS-PP manufactured by Sun Allomer Co., Ltd.) is preferable from the viewpoint of excellent foamability. In particular, as a raw material polypropylene resin, a propylene homopolymer, a block or random polymer of propylene and another monomer, and the like can be raised, and a propylene homopolymer is preferable in terms of rigidity and cost. The raw material polypropylene resin may be mixed with other thermoplastic resins such as polyethylene as long as the foamability is not impaired. Additives such as antioxidants, metal deactivators, fluorescent brighteners, UV stabilizers and antistatic agents may be added.

  The polypropylene resin foam sheet in the present invention is prepared by mixing a raw material polypropylene resin, a nucleating agent and a foaming agent, then adjusting the melt kneading / foaming suitable temperature in an extruder, and using a circular die having an annular lip, Easily by extruding from the lip of the die into the atmospheric pressure to obtain a cylindrical foam, and then drawing the cylindrical foam with a cooling cylinder (mandrel) and then cutting it after drawing and cooling to form a sheet To be manufactured. Further, extrusion foaming may be performed continuously or in parallel with the production of the raw material polypropylene resin. Examples of the nucleating agent include sodium bicarbonate, citric acid, talc and the like. The addition amount of the nucleating agent is not particularly limited, but since the thickness of the foamed sheet is preferably 1 to 5 mm, it is 0.01 to 3 parts by weight to obtain bubbles necessary for adjusting the thickness. The number of bubbles is preferably 5 to 15 in the thickness direction from the viewpoint of surface properties. In addition to the number of bubbles, the thickness can be adjusted by the amount of foaming agent. Examples of blowing agents include aliphatic hydrocarbons such as butane and propane, alicyclic hydrocarbons such as cyclobutane and cyclopropane, halogenated hydrocarbons such as chlorodifluoroethane and tetrafluoroethane, inorganic gases such as carbon dioxide and nitrogen, water These may be mentioned, and one or two of them may be combined. Although the addition amount of a foaming agent changes with kinds of foaming agent and the target thickness, 0.5-10 weight part is preferable in order to adjust thickness similarly to the said nucleating agent addition amount.

  A container made of a polypropylene-based laminated foamed sheet can be obtained by thermoforming the polypropylene-based laminated foamed sheet of the present invention by a known molding technique such as vacuum molding, pressure forming, plug molding, match molding, or the like.

  The container made of the polypropylene-based laminated foam sheet of the present invention is peeled into a polypropylene-based film and a polypropylene-based foamed sheet molded product. At the time of peeling, the polypropylene resin layer molded product which is an extrusion laminate layer is laminated on the polypropylene foamed sheet molded product, and is peeled off at the film / printing ink interface.

  In order to peel, it is necessary that the peel strength between the printing ink adhered to the polypropylene resin foam sheet side and the polypropylene resin film is 0.3 to 1.5 N / 15 mm. If the peel strength is less than 0.3 N / 15 mm, the film may be peeled off during molding and heating. If the peel strength is 1.5 N / 15 mm or more, the peel strength is high and simple peeling is not possible.

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

(Example 1)
(Method for producing polypropylene resin foam sheet A)
A biaxial extrusion of a blended mixture of 100 parts by weight of a polypropylene homopolymer (Prime Polymer J105) and 0.3 parts by weight of a radical polymerization initiator (t-butylperoxyisopropyl monocarbonate) with a ribbon blender. To the machine, 0.5 parts by weight of isoprene is supplied from the middle of the extruder using a liquid pump, melt-kneaded in the twin-screw extruder, and melt-extruded to obtain a modified polypropylene resin composition. Pellets were obtained. The twin screw extruder was of the same direction twin screw type, the screw diameter was 44 mmφ, and the maximum effective length (L / D) was 38. The set temperature of the cylinder part of this twin-screw extruder was set to 180 ° C. until isoprene monomer injection, 200 ° C. after isoprene injection, and the screw rotation speed was set to 150 rpm. 65 polypropylene resin compositions obtained by stirring and mixing 100 parts by weight of a modified polypropylene resin in the previous period, 0.05 parts by weight of blended oil, and 0.5 parts by weight of a nucleating agent (Celbon SC / K manufactured by Eiwa Kogyo Co., Ltd.) using a ribbon blender. After supplying to a -90 mmφ tandem type extruder and melting in a first stage extruder (65 mmφ) set at 200 ° C., a mixed gas of isobutane and normal butane (isobutane ratio 85%) is used as the blowing agent. 1.5 parts by weight of 100 parts by weight of the resin composition, and cooled in a second stage extruder (90 mmφ) set at 160 ° C. (measured by a temperature sensor installed in the resin inflow part of the die), 4.6m while being discharged from a circular die (75mmφ) under atmospheric pressure and molded in a cooling cylinder with an outer diameter of 200mm and a body length of 800mm / Min to obtain a drawn-cooled cylindrical foam while drawing by which to obtain a foamed sheet of 635mm width by cutting open with a cutter. The obtained foamed sheet has a density of 0.182 g / cc (measured according to JIS-K6767), a closed cell ratio of 77% (measured with an air pycnometer according to ASTM D2856), an average thickness of 1.8 mm, and a basis weight. It was 280 g / m ² and the number of bubbles was 10 / thickness.
(Method for producing polypropylene-based printing film A)
Using two gravure plates with a plate depth of 30 μm on the corona-treated surface of a 25 μm-thick biaxially stretched polypropylene film (MF-20 manufactured by Santox), printing ink (Lamic NA manufactured by Dainichi Seika Co., Ltd.), red, orange After applying the color by the gravure method, the residual solvent was removed by drying to obtain a polypropylene-based printing film. The amount of printing ink applied was 6 g / m ² for the two colors.

(Method for measuring the amount of printing ink applied)
A 10 × 10 cm film sample was cut out from the printing film, the weight of the printing ink scum was measured, and the coating weight of the printing ink was obtained by subtracting the 10 × 10 cm square film weight of the unprinted film.

(Production method of polypropylene resin laminated foam sheet)
The polypropylene resin foam sheet is fed out at a speed of 18 m / min. At the same time, a polypropylene resin (Prime Polymer's J105G) is extruded from a T-shaped die at a thickness of 70 μm perpendicular to the flow direction of the foamed sheet, and at the same time, the polypropylene printed film A is fed out from the opposite side of the foamed sheet and pressed with a nip roll. While taking it up, a three-layer polypropylene-based laminated foam sheet was obtained.

(Measurement of peel strength of polypropylene-based laminated foam sheet)
The measurement of the interlayer strength of the obtained polypropylene resin laminated foam sheet and the polypropylene resin layer / polypropylene resin foam sheet was measured according to JIS Z0237. The measurement was performed by cutting out a test piece having a width of 15 mm from the laminated foamed sheet with a cutter, peeling the laminated film in an appropriate amount in parallel with the short piece, and pulling the peeled film with an orientec autograph at a pulling rate of 100 mm / min. , 90 ° peeling was performed, and the peel strength was measured.

(Manufacturing method of container)
The polypropylene-based laminated foamed sheet is cut into 540 × 540 mm squares, and fixed to a frame having an inner size of 500 mm × 500 mm using a single molding machine (VAF-66-45T manufactured by SENBA System Co., Ltd.), and then the ambient temperature is 250 ° C. The container obtained by inserting into a heating furnace adjusted to 30 seconds and then taking out and fitting with a match mold was cut with a Thomson blade to obtain a round container of φ200.

(Appearance evaluation of containers)
The film lamination surface of the container was observed and evaluated according to the following criteria.
○: The film is not peeled off from the laminated foam sheet (the film is not lifted). Particular attention was paid to the outer peripheral end surface of the container and the Thomson blade cutting surface.
X: The film is peeled off from the laminated foam sheet (the film can be lifted).

(Evaluation of peelability of film from container)
Nitto Denko cloth adhesive tape NO. 75 was adhered, and the film state when the cloth adhesive tape was pulled from the end face was observed and evaluated according to the following criteria.
○: The film peels from the laminated foam sheet.
X: The film does not peel from the laminated foam sheet, but peels only the adhesive tape.

(Example 2)
A polypropylene resin laminated foam sheet was obtained in the same manner as in Example 1 except for the method for producing the polypropylene film B.
(Method for producing polypropylene-based printing film B)
Using a gravure plate with a plate depth of 30 μm on the corona-treated surface of a 25 μm-thick biaxially stretched polypropylene film (MF-20 manufactured by Santox Co., Ltd.), printing ink (Lamic NA manufactured by Dainichi Seika Co., Ltd.) and brown by gravure method After coating, the residual solvent was removed by drying to obtain a polypropylene-based printing film. The amount of printing ink applied was 3 g / m ² .

(Comparative Example 1)
A polypropylene resin laminated foam sheet was obtained in the same manner except that a biaxially stretched polypropylene film (MF-20 manufactured by Santox Co., Ltd.) having a plain thickness of 25 μm was used for the polypropylene film for lamination.

(Comparative Example 2)
A polypropylene resin laminated foam sheet was obtained in the same manner as in Example 1 except for the method for producing the polypropylene film C.
(Method for producing polypropylene-based printing film C)
Using a gravure plate with a plate depth of 30 μm on the corona-treated surface of a 25 μm thick biaxially oriented polypropylene film (MF-20 manufactured by Santox Co., Ltd.) After coating by the method, the residual solvent was removed by drying to obtain a polypropylene-based printing film. The amount of printing ink applied was 3 g / m ² .

(Comparative Example 3)
A polypropylene resin laminated foam sheet was obtained in the same manner as in Example 1 except for the method for producing the polypropylene film D.
(Method for producing polypropylene-based printing film D)
Using 3 plates of gravure plate with a plate depth of 30μm on the corona-treated surface of 25μm thick biaxially oriented polypropylene film (MF-20 manufactured by Santox Co., Ltd.) After applying brown and white by the gravure method, the residual solvent was removed by drying to obtain a polypropylene-based printing film. The amount of printing ink applied was 9 g / m ² .

  Table 1 shows the evaluation results of the polypropylene-based laminated resin foam sheets in Examples 1 and 2 and Comparative Examples 1 to 3. By adjusting the amount of printing ink applied and the peel strength of the laminated film by adjusting the printing film laminating conditions, a container that does not peel off the film before use of the container and can be easily peeled off after use of the container is formed. A polypropylene-based resin laminated foam sheet can be obtained.

Claims (3)

  A polypropylene resin laminated foam sheet in which a polypropylene resin film printed on a polypropylene resin foam sheet is laminated so that the printing surface is on the inside (foam sheet side), and the printed layer adheres to the polypropylene resin foam sheet side A method for producing a polypropylene-based laminated foamed sheet, wherein the polypropylene-based resin film is laminated by extrusion lamination with a polypropylene-based resin so that the peel strength between the resin and the polypropylene-based resin film is 0.3 N to 1.5 N / 15 mm.   The method for producing a polypropylene-based resin laminated sheet according to claim 1, wherein the printed layer is made of an ink based on a resin made of chlorinated polypropylene, chlorinated EVA or a mixture. Method for producing a polypropylene laminated foam sheet according to claim 1 and 2, wherein the coating amount of the printing ink is 1 to 7 g / m ^2.