JPH027814B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for attaching a label to a molded article within a mold during blow molding, injection molding, pressure forming or vacuum forming. A thermoplastic resin film made of polyvinyl chloride, polypropylene, polyethylene, etc. printed with letters or designs is cut out, fixed in a mold by electrostatic adhesion or reduced pressure, and then a melted thermoplastic resin of the same material as the film is cut out. There is a known method for producing a thermoplastic synthetic resin molded product with a label pasted or painted on it by bringing it into contact with a film under pressure or reduced pressure and then cooling the melt (Japanese Patent Publication No. 28-5036).
No. 38-26119, No. 40-12988, No. 46-9959
No. 48-12865, etc.). Injection molded products, blow molded products, vacuum molded products, etc. using these printed thermoplastic resin films as labels are attached at the time of molding, so the adhesion between the label and the molded product is strong. Furthermore, since the material of the label is made of a highly water-resistant thermoplastic resin film, it is particularly useful as hollow liquid containers for detergents, shampoos, antifreeze, medicine bottles, and the like. However, in conventional label pasting (including painting) methods, the label material and the molding resin for hollow, injection, etc. are the same resin, so the label melts during molding, causing the criticality of the printed characters and designs. The image often becomes blurred and unclear. Fortunately, conventional label film printing is gravure printing or flexographic printing, and these printing methods can only print large, simple designs and letters, so overall the printing is slightly blurred due to melting of the label during molding. The reality is that the label was saved as there was no practical problem, and there is hope for a plastic label that can be printed with delicate letters and designs in multiple colors and that can be attached during molding. Offset printing is useful as a printing technique because it allows delicate characters and designs to be printed in multiple colors, but it has the disadvantage that it cannot be applied to conventional plastic film for labels. Recently, synthetic papers with paper-like layers made of stretched polypropylene films or polyethylene films containing inorganic fillers have been proposed or commercially available (Japanese Patent Publications No. 46-40794, No. 54-31030,
(Refer to BP1090059 publications) There is also synthetic paper that can be offset printed. This offset printable synthetic paper is fixed in a mold as a label, and the same material resin as the label is used for blow molding, pressure molding, etc.
If low-pressure molding at ~8 kg/cm ² is performed, the label will shrink during molding and wrinkles will occur, resulting in only defective products. This is because the label is a stretched film, so the external stress stored during stretching becomes shrinkage stress, and when it comes into contact with molten resin during blow molding or other molding, the heat causes the label to shrink. The present inventors manufactured various labels to prevent wrinkles when using this stretched film as a label, and as a result of studying the method of attaching the labels, the inventors determined that the material resin for the label should be used as the resin to be molded. By using a thermoplastic resin that has a melting point 15°C or more lower than the melting point, and by using the same type of resin as the molding resin as the film material that makes up the back layer of the label, it is possible to prevent the occurrence of wrinkles on the label, and They discovered that a thermoplastic synthetic resin molded product having characters, designs, patterns, etc., in which a label and a molded product are strongly adhered to each other can be obtained, and the present invention was completed. That is, in the present invention, a stretched polypropylene film containing 8 to 65% by weight of inorganic fine powder with offset printing on the surface is used as a paper-like layer, and the surface opposite to this paper-like layer is made of polyethylene. A composite film with a two-layer structure in which the back layer is a film with a thickness of 1 to 10 microns, or a multi-layer structure in which a base layer made of a biaxially stretched polypropylene film is provided between the paper-like layer and the back layer. A label made of a composite film with a wall thickness of 30 to 300 microns is fixed so that the paper layer side of the label is in contact with a mold, and then molten polyethylene is attached to the back layer side of the label under pressure or reduced pressure. The present invention provides a method for attaching a label, which is characterized in that the polyethylene is cooled. In the practice of the present invention, the simplest structure of the multi-layer label before offset printing is 8 to 65% by weight of inorganic filler, preferably 20 to 55% by weight.
The paper-like layer is made of a stretched polypropylene film and has a wall thickness of 1 to 10 microns (μ), preferably 3
~10μ polyethylene with density 0.91~0.97g/cc,
Preferably, the back layer is made of medium-low density or high-density polyethylene with a density of 0.935 to 0.960 g/cc.
It is a composite film with a two-layer laminated structure of 30 to 300μ, preferably 35 to 100μ. Such a composite film is produced by melting and kneading polypropylene containing an inorganic filler and the polyethylene in separate extruders, feeding them into the same die, laminating them in the die, and coextruding them into a sheet.
After cooling to 80℃, 134-164℃, preferably 145-160
℃, and biaxially stretched 3.5 to 10 times in the longitudinal and lateral directions simultaneously or sequentially, and if necessary, annealing the obtained stretched film at 165 to 168℃ for 5 to 60 seconds. It will be done. In addition, a polypropylene film containing an inorganic filler was preliminarily coated using the difference in circumferential speed of the roll group.
The polyethylene film is melt-laminated on the film obtained by longitudinal stretching 3.5 to 7 times at ~155°C, cooled once to 50 to 80°C, and then reheated to 134 to 164°C, preferably 155 to 164°C. It is obtained by heating and then stretching 4 to 10 times in the transverse direction using a tenter. In this method for producing a multilayer film as well as in the method for producing a composite film having three or more layers described below, the annealing treatment is performed as necessary after stretching. When the composite film has three or more layers, it can be manufactured in various ways. For example (A). 8 inorganic fine powders
Polypropylene containing ~65% by weight, (B). Polypropylene, (C). Polyethylene with a density of 0.91 to 0.97 g/cc, preferably 0.935 to 0.970 g/cc, is melted and kneaded using separate extruders, and the melt is
The film made of (B) is laminated in the die so that it becomes an intermediate layer, and the co-extruded laminated sheet is heated at a temperature lower than the melting point of the polypropylene (A), either simultaneously or sequentially. Manufactured by axial stretching. In addition, after longitudinally stretching the coextruded sheet of polypropylene (B) and polyethylene (C) in advance,
It can also be obtained by laminating a sheet of the polypropylene composition (A) on the surface side of the polypropylene sheet (B) of this coextended sheet, and then laterally stretching the sheet. Furthermore, a sheet of the polypropylene composition (A) and a sheet of polyethylene (C) are melt-laminated on each side of the polypropylene sheet (B), which has been longitudinally stretched in advance, and then laterally stretched. You can get it no matter what. When coextruding the polyethylene layer and the polypropylene layer, a coextruded sheet with uniform thickness distribution can be obtained by containing 5 to 25% by weight of polyethylene on the polypropylene layer side. Among these multilayer films, from the viewpoint of offset printability, it is preferable that the paper-like layer of polypropylene containing 8 to 65% by weight of inorganic fine powder is oriented only in one axis direction. By stretching, cracks are generated on the surface with the inorganic fine powder as the nucleus, and the adhesion and drying properties of the printing ink are improved. Biaxially stretched orientation increases the chances of inorganic fine powder falling off, and deep cracks formed by uniaxial stretching may disappear with further stretching, resulting in offset printability inferior to uniaxially oriented films. . Further, the number of layers is preferably three or more including a biaxially oriented polypropylene film layer as an intermediate layer. This biaxially oriented polypropylene film gives stiffness to the label and facilitates paper feeding during sheet offset printing. The wall thickness of the label used in the pasting method of the present invention is
30 to 300μ, preferably 45 to 100μ, and
The thickness of the back layer is 1-10μ, preferably 3-10μ. If the label thickness is thinner than 30μ, paper feeding and offset printing will be difficult. Additionally, the label may shrink during molding. If the wall thickness exceeds 300μ, it is economically disadvantageous. The thickness of the polyethylene film on the back layer is 1μ because the polyethylene film is melted by the heat of the molten polyethylene during injection and blow molding, and the molded product and label are strongly adhered to each other.
The above is necessary. Moreover, if it exceeds 10μ, the label will curl, making offset printing difficult or fixing the label to the mold, which is not preferable. The label can be secured to the mold using conventional electrostatic adhesion methods or reduced pressure (vacuum) methods. Examples of the molding method include blow molding, injection molding, pressure molding, vacuum molding, and the like. During the molding process, the labels are made of molten polyethylene parison,
The paper-like layer side of the label, which is in contact with the sheet but has offset printing, is cooled by contacting the mold, so the surface of the paper-like layer does not melt. That is, multicolor printing does not lose its clarity. Further, since the label is attached to the molten polyethylene molded body under pressure and in a state in which the polypropylene of the paper-like layer of the label is not entirely melted, shrinkage of the label is prevented. The temperature of molten polyethylene during labeling is 180-230℃ for blow molding and 190℃ for injection molding.
~250℃, 175~ for pressure forming or vacuum forming
The temperature is 230℃. The pressure is 1.5 for hollow molding and pressure molding.
-10Kg/ ^cm2 , injection molding 20-200Kg/ ^cm2 , vacuum forming 2-600mmHg. According to the label attaching method of the present invention, the label can be strongly attached to the molded article without problems such as heat shrinkage or unclear printing, even though a stretched film is used. . Furthermore, since polyethylene and polypropylene, which are highly water and chemical resistant, are used as the label material, even if the molded product obtained by implementing the present invention is used as a container for liquids such as shampoo, frozen liquid, motor oil, etc., the label will not be removed from the container body. It won't peel off. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example of manufacturing synthetic paper 1 (B). Mitsubishi Yuka Co., Ltd.'s polypropylene "Mitsubishi Noblen MA-6" (trade name, melting point = 164℃) 87 parts, Mitsubishi Yuka Co., Ltd.'s high-density polyethylene "Yukalon Hard"
EY-40” (product name, melting point = 130℃, density 0.950g/
After melt-kneading a composition consisting of 10 parts of cc) and 3 parts of fired clay using an extruder, 250 parts of
The sheet was extruded at a temperature of 50°C and the sheet was cooled to a temperature of about 50°C. Next, after heating this sheet to about 153℃,
A uniaxially stretched film was obtained by stretching 4 times in the longitudinal direction using the difference in peripheral speed between the roll groups. Separately, (A). Polypropylene “Mitsubishi Noblen MA-3” manufactured by Mitsubishi Yuka Co., Ltd. (trade name, melting point = 163℃) 57
(C) and 43 parts of calcined clay. High-density polyethylene "Yukalon Hard EY-40"
Melt and knead using two separate extruders,
From two dies, extrude the melted material (A) at a temperature of 250°C and the polyethylene (C) at a temperature of 230°C into sheets, respectively, and laminate them on the front and back surfaces of the uniaxially stretched film to obtain a three-layer sheet. Ta. After cooling this three-layer sheet to 60℃, approx.
The film was reheated to a temperature of 163°C, stretched 8 times in the transverse direction using a tenter, and then passed through an oven set at 165°C to set the heat.
℃, and the edges were slit to obtain an intermediate biaxially stretched base layer film with a thickness of 62 microns, a surface layer uniaxially stretched film made of the composition of (A) with a wall thickness of 20 microns, and (C A composite stretched film [] having a thickness of 8 microns in the back layer made of polyethylene was obtained. Examples 2 to 5 Composite stretching was carried out in the same manner as in Example 1 above, except that the slit width of the die was changed so that a composite stretched film in which the thickness of the back layer made of the uniaxially stretched polyethylene film of (C) was as shown in Table 1 was obtained. Film〔〕〜
I got []. Example 6 The compositions (A), (B), and (C) used in Example 1 were melt-kneaded using separate extruders, fed to one die, and (B) was mixed in the die. A sheet made of the composition was laminated to serve as an intermediate layer, and then coextruded at 230°C to obtain a three-layer sheet. Once this three-layer sheet was cooled to 60℃, it was heated to 135℃.
The paper-like paper (A) A composite stretched film was obtained in which the layer thickness was 20 microns, the base layer (B) had a thickness of 62 microns, and the back layer (C) had a thickness of 8 microns. Example 7 (C) High density polyethylene (melting point 134℃) and (A)
MI4.0 polypropylene (melting point 164℃) 51% by weight,
A composition obtained by mixing 45% by weight of calcium carbonate with an average particle size of 1.5μ and a specific surface area of 1.8m ² /g and 4% by weight of maleic anhydride grafted polypropylene was melt-kneaded in a separate extruder and laminated in a die. 210℃
After cooling the coextruded sheet to 60℃,
Heat to 158℃, then crosswise for 5 minutes using a tenter.
multiplied and then annealed at 160 °C for 60
It was cooled to 0.degree. C. and the edges were slit to obtain C/A two-layer synthetic paper (thickness: 8 .mu.m/92 .mu.m). Label Production Examples 1 to 7 After the paper-like layer side of the synthetic paper (composite stretched film) obtained in Production Examples 1 to 7 was subjected to corona discharge treatment, an acrylic antistatic agent manufactured by Mitsubishi Yuka Co., Ltd. was applied to the surface thereof. solution
ST-1300 was applied and dried. Next, the edges of the composite stretched film were slit, and the composite stretched film was further cut into a width of 50 cm using a knife cutter perpendicular to the film flow direction, and the cut composite stretched film was stored in a sheet stocker. After multicolor offset printing was performed on the paper-like layer surface of the cut sheet-like synthetic paper according to each purpose, the printed portion was trimmed to obtain a label. Examples and Comparative Examples Evaluation of synthetic paper and labels Offset printability: Number of sheets printed at which fine inorganic powder falls off from the surface of synthetic paper, making continuous printing difficult. Curling property: When a piece of synthetic paper measuring 300 mm long and 300 mm wide was placed on a flat plate with the back layer facing up, it was evaluated as follows based on the height of the raised corners of the synthetic paper. ◎: Excellent (0 mm) ○: Good (more than 0 and less than 1 mm) △: Practical (more than 1 mm and less than 2 mm) ×: Poor (more than 2 mm) Adhesiveness: Label [ ] is pasted using the following molding method. A molded product was manufactured. The presence or absence of deformation of the label of the obtained molded product was investigated (○ - not present, × - present). The adhesive strength between the molded body and the label was strong, and the label could not be peeled off by hand. Blow molding A label measuring 50 mm in length and 70 mm in width is fixed by vacuum decompression with the paper layer side in contact with the mold, and then molded into Mitsubishi Yuka.
High-density polyethylene “Yukalon Hard EY−” manufactured by Co., Ltd.
40'' is extruded into a parison shape at 230°C, and then the parison is sandwiched between molds, and then compressed air with a pressure of 5 kg/cm ² is supplied into the parison to form it, and the molded body is cooled by the mold, and then Open trunk diameter 60
A hollow container (wall thickness: 1 mm) with a height of 200 mm and a height of 200 mm was obtained. Injection molding After inducing static electricity on a pentahedral label with a side length of 50 mm and fixing the label to the inner surface of the injection mold using electrical attraction, the polyethylene Yucalon Hard EY
-40'' was injection molded at 240℃ and a pressure of 100Kg/ ^cm2 .
After cooling for 2 minutes, a rectangular prismatic container (wall thickness: 2 mm) whose entire surface was decorated was obtained. Vacuum forming After inducing static electricity on a 20 mm long and 40 mm wide label and fixing the label in the female mold using electrical attraction, a polyethylene "Yukalon Hard EY-40" sheet (thickness 0.6 mm) is heated to 190°C. After guiding it onto the mold, the tip was vacuum-formed with the aid of a plug under reduced pressure of 45 mmHg. Changes in printing Discoloration of the print on the label attached to the molded product was observed. (○ - No fading. △ - Slight fading, but no practical problem. × - Label was deformed, so no observation was made.) [Table]

Claims (1)

[Claims] 1 A stretched polypropylene film containing 8 to 65% by weight of inorganic fine powder is used as a paper-like layer, and a polyethylene film with a thickness of 1 to 10 microns forming the surface opposite to this paper-like layer is used as a back layer. A label with a wall thickness of 30 to 300 microns made of a two-layer composite film, or a multi-layer composite film with a base layer made of a biaxially stretched polypropylene film between the paper-like layer and the back layer. of,
A label characterized in that the paper-like layer side of the label is fixed in contact with a mold, then molten polyethylene is applied to the back layer side of the label under pressure or reduced pressure, and then the polyethylene is cooled. Pasting method.