JPH0284319A - Production of synthetic paper for label use - Google Patents

Abstract

PURPOSE:To reduce a lowering of stiffness strength by applying emboss processing to the heat-sealable resin layer of a film having a double-layer structure before stretching and subsequently stretching the embossed film. CONSTITUTION:A resin film prepared by containing 8-65wt.% of a fine inorg. powder with a resin having an m.p. of 135-264 deg.C such as polypropylene or high density polyethylene is used as the base material layer 2 of a label for a container. A film layer 4 composed of a heat-sealable resin having an m.p. of 85-135 deg.C such as low density polyethylene or a vinyl acetate/ethylene copolymer is provided to the rear of the resin film of the base material layer and subjected to emboss processing by a metal roll and a rubber roll. The stretching of the film having a double-layer structure after emboss processing is performed at a temp. range from temp. lower than the m.p. of the resin of the base material layer and temp. equal to or more than the m.p. of the heat-sealable resin. The base material layer is oriented by stretching but the heat-sealable layer is not oriented.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to the production of synthetic paper used for labels (including blanks) to be attached to synthetic resin containers produced by differential pressure molding or blow molding. Regarding the method, in particular, a label is set in advance in a mold, and a thermoplastic resin is blow-molded, vacuum-formed, or pressure-formed on the label, thereby integrally molding a resin-molded container with a label to decorate the container. This paper relates to a method for producing synthetic paper used for container labels.

[Conventional technology]

Conventionally, in order to integrally mold resin molded containers with labels,
A blank or a label is inserted into a mold in advance, and then a container is formed by injection molding, blow molding, differential pressure molding, foam molding, etc., and the container is decorated. Such labels include gravure-printed resin film, offset multi-color printed synthetic paper (for example, Tokko Kokko 1986-40
794, Japanese Patent Publication No. 54-31030, British Patent No. 1,090,059, etc.), or aluminum labels in which polyethylene is laminated on the back side of aluminum foil and gravure printing is performed on the surface of the foil.

However, the manufacturing method of resin-molded containers decorated with the above-mentioned labels and blanks is limited to high-pressure (10
0 to 1000 kg/cm"), a method of welding molten resin containers in a planned manner yields a product with a good appearance, but
Differential pressure molding (2 to 7 kg/cm”) and hollow molding (1 to 10 kg/cm”)
In the method of molding at a low pressure such as 100 kg/cm''), air escape between the blank and the melting container is not sufficient, and blisters are generated here and there between the container and the blank, which impairs the appearance of the container.

In view of the above-mentioned problems, we have developed an embossing process on the back side of labels (including blanks) to make it easier to release air between the label and the container, thereby preventing the occurrence of blisters. (Utility Application No. 63-1775).

That is, in this label, a heat-sealable resin layer having a melting point lower than the melting point of the material resin of the film is provided on the back side of a thermoplastic resin film whose surface is printed,
This is a container label in which the heat-sealable resin layer is embossed with 5 to 25 lines per inch.

[Problems to be Solved by the Invention] In order to impart stiffness to thin labels, stretching orientation has been applied to a multilayer structure film for labels (see Examples of the same application). This stretching orientation is performed before embossing.

When synthetic paper is embossed after stretching and orientation, the depth h of the embossments tends to increase, and the stiffness of the label, which has been increased by stretching, is slightly reduced.

If the label does not have a certain degree of stiffness, mistakes will occur in the process of suctioning the label with the suction cup of the automatic feeder and inserting it into the mold.

The object of the present invention is to provide a synthetic paper for embossed labels with little reduction in stiffness.

[Specific means to solve the problem]

In the present invention, the heat-sealable resin layer side of the multilayer structure film is embossed before stretching, and then stretched.

That is, the present invention provides a multilayer structure film by providing a heat-sealable resin layer having a melting point lower than the melting point of the material resin of the film on the back side of a thermoplastic resin film containing inorganic fine powder, and After embossing the layer, the multilayer structure film is stretched at a temperature higher than the melting point of the heat-sealable resin but lower than the melting point of the resin of the thermoplastic resin film containing inorganic fine powder. The present invention provides a method for producing a synthetic material for labels.

Hereinafter, in order to explain the label for a molded container in more detail, a blank for a differential pressure molded container will be specifically described below as an example of the present invention.

FIG. 1 shows a sectional view of an inner mold label for blow molding manufactured as an example of the present invention, in which 1 is a label, 2 is a thermoplastic resin film base layer, 3 is printing, and 4 is heat sealing. The heat-sealing resin layer 5 is a diaphragm (5) in which a tod-like diaphragm pattern is given to the heat-sealable resin layer by embossing.
It shows the top of the dot. 6 is the valley of the aperture.

FIG. 2 shows the label 1 on the heat-sealable resin layer 4 side (
FIG. 3 is a plan view of the back side of the label. FIG. 3 is a cross-sectional view of the multilayer structure film before stretching and printing to obtain the label shown in FIG. 1, and FIG. 4 is a partially enlarged view of the multilayer structure film shown in FIG. 3.

The embossed pattern of the multilayer structure film shown in Fig. 3 is
For example, the number of dots or lines is 5 to 200, preferably 15 to 120 per inch (2.54 cm). The number of dots or lines per inch is called the number of lines, and is a measure of the fineness or roughness of the embossed pattern.

The depth (h) of the valleys of the embossed pattern is 1/3 or more, preferably 1/2 or more of the wall thickness (ho) of the heat-sealing resin layer 4, and may be embedded into the base material layer 2 (h> h,).

By stretching this embossed multilayer structure film at least 4 to 12 times in one direction, the thickness of the multilayer structure film is reduced, and the embossed pattern becomes wider and the depth of the embossed valleys becomes shallower. It is preferable that the heat-sealable resin layer has a surface smoothness (JISP-8119) of 1 to 1000 seconds and an average surface roughness (Ra) of 0.5 to 5 microns.

The base material layer 2 of the container label is made of polypropylene, high-density polyethylene, polyvinyl chloride, polyethylene terephthalate, polyamide, etc., with a melting point of 135 to 264°.
Even if it is a resin film containing 8 to 65% by weight of inorganic fine powder in the resin of C, a film in which latex containing an inorganic filler is coated on the surface of the resin film, or a film in which aluminum is vapor-deposited on the film. good.

The back side of the resin film of these base material layers (the side in contact with the resin container) is coated with low-density polyethylene, vinyl acetate/ethylene copolymer, ethylene/acrylic acid copolymer, ethylene/
Metal salts of methacrylic acid copolymers, etc., with a melting point of 85 to 13
A film layer 4 of heat-sealable resin at 5 DEG C. is provided and embossed with a metal roll and a rubber roll.

This heat-sealable resin layer can further strengthen the adhesion between the label and the resin container.

The multilayer structure film after embossing is stretched at a temperature lower than the melting point of the resin of the base layer and higher than the melting point of the heat-sealable resin. The base material layer is oriented by stretching,
The heat seal layer is not oriented.

The base material layer 2 may be a single layer or may have a multilayer structure of two or more layers.

The stretched multilayer structure film (synthetic paper) can be subjected to corona discharge machining, flame treatment, plasma treatment, etc. to improve its surface printability and adhesiveness, if necessary.

For printing, there are methods such as gravure printing, offset printing, flexo printing, and screen printing, and barcodes, manufacturer, sales company names, characters, product names, usage instructions, etc. are printed.

The printed and embossed container label 1 is separated into labels of required shapes and dimensions by punching. This label may be a partial label attached to a part of the container surface, but usually it is a blank that surrounds the side of a cup-shaped container, and in blow molding, it is attached to the front and back of a dish-shaped container. It is manufactured as a label.

(Molding) After installing the label l in the lower female mold cavity of the differential pressure molding mold so that the printed side is in contact with the cavity surface of the mold, the label is fixed to the inner wall of the mold by the suction of the mold. Next, the molten sheet of container molding material resin is guided above the lower female mold and differential pressure molded by a conventional method to form a container with a label integrally fused to the outer wall of the container.

Although both vacuum forming and air pressure forming can be used for differential pressure forming, differential pressure forming using a combination of both and using plug assist is generally used. The label can also be applied to blow molding, in which a molten resin parison is pressed onto the inner wall of a mold using compressed air.

In the container molded in this way, after the label 1 is fixed in the mold, the label and the resin container are integrally molded, so there is no deformation of the label 1, and the adhesion between the container body 4 and the label 1 is strong. The container is strong, has no blisters, and has a good appearance decorated with a label.

Example 1 Melt flow rate (MFR) 0.8, melting point 164°C
70% by weight of homopolypropylene, 12% by weight of high-density polyethylene with a melting point of 134°C, and 18% by weight of heavy calcium carbonate with an average particle size of 1.5 μm (A),
After kneading in an extruder set at °C, the mixture was extruded into a sheet and cooled in a cooling device to obtain a non-stretched sheet.

After heating this sheet to 145°C, it was stretched 5 times in the machine direction.

On the other hand, 58% by weight of homopolypropylene with an MFR of 4.0
A mixture (B) of 42% by weight of calcium carbonate with an average particle size of 1.5 μm, and low density polyethylene (C) with a melting point of 117 °C are melt-kneaded at 270 °C using separate extruders, -The above (A)
The back side of the sheet stretched 5 times in the longitudinal direction of
(line), dots with a valley depth of 30 μm were embossed.

On the other hand, the mixture of (B) above was laminated on the surface side of the sheet of (A) to obtain a film with a multilayer structure.

Next, this multilayer structure film was reheated to about 155°C, stretched 7 times in the transverse direction, and then corona discharge treated to the paper-like layer (B), cooled to 55°C, and the edges were By slitting, a four-layer synthetic paper with each layer (B)/(A)/(B)/(C) having a thickness of 30/70/30/loum was obtained.

Offset printing is applied to the paper-like layer (B) side of this synthetic paper,
Next, this was punched to form a label for hollow molding (width 60mm).
mm, length: 110 mm).

The smoothness of the (C) layer of this label is 110 seconds, and the average surface roughness (Ra) is 1.2 microns, JIS-P-8125.
Dever stiffness measured in MD force direction is 1.8 g-cm
, TD force direction was 3.5 g-cm.

After fixing this label to one side of a blow molding mold using a vacuum so that the printed side (B) is in contact with the mold, a parison of high density polyethylene (melting point 134°C) is
After melt extrusion at ℃ and then clamping the split mold, 4.2 k
g/cm'' was supplied into the parison to expand the parison into a container shape and fuse it with the label.The mold was then cooled and opened to obtain a hollow container.

In this hollow container, there was no fading of the print, and no label shrinkage or blister formation was observed. In addition, the supply of labels to the split mold for blow molding using an automatic label feeding device is 1
00 sheets in a row, but the label fell off due to mistake C type, etc.)
Not once.

Reference example Melt flow rate (MFR) 0.8, melting point 164°C
70% by weight of homopolypropylene, 12% by weight of high-density polyethylene and 1% calcium carbonate with an average particle size of 1.5 μm.
8% by weight of (A) was blended, kneaded in an extruder set at 270°C, extruded into a sheet, and cooled in a cooling device to obtain a non-stretched sheet. Heat this sheet to 145°C
After heating, the film was stretched 5 times in the longitudinal direction.

On the other hand, 58% by weight of homopolypropylene with an MFR of 4.0
A mixture (B) of 42% by weight of calcium carbonate with an average particle size of 1.5 μm, and low density polyethylene (C) with a melting point of 117 °C are melt-kneaded at 270 °C using separate extruders, -The above (A)
It was extrusion laminated on the back side of a sheet stretched 5 times in the longitudinal direction.

On the other hand, the mixture of (B) above is laminated on the front side of the sheet of (A), and then this multilayer sheet is heated at 155°.
After reheating to 55"C, it was stretched 7 times in the transverse direction, then subjected to corona discharge treatment, cooled to 55"C, and the edges were slit to form (B)/(A)/(B)/(C ) A four-layer synthetic paper with each layer having a thickness of 30/70/30/10 μm was obtained.

This synthetic paper paper J'! After applying offset printing to the (B) side, pass it through an embossing roll at 1.27 mm intervals (
20 lines), dots with a valley depth of 8 μm were embossed on the (C) side of the synthetic paper.

Next, this was punched to form a label for hollow molding (width 60mm).
110 mm in height). The Dever stiffness of this label was 1.3 in the MD force direction and 3.1 g-cm in the TD force direction.

After fixing this label to one side of a split mold for blow molding using a vacuum so that the printed surface is in contact with the mold, a parison of high-density polyethylene (melting point 134°C) is melt-extruded at 190°C, and then split. After clamping the mold, 4.2kg/cm
'' was supplied into the parison to expand the parison into a container shape and fuse it with the label.The mold was then cooled and opened to obtain a hollow container.

This hollow container had no discoloration in the print, and no signs of label shrinkage or blistering, but when the labels were automatically fed into the blow molding die, 25 out of 100 labels were fed incorrectly. .

Example 2 20 parts of resin composition (A) containing 40 parts of polypropylene, 25 parts of high-density polyethylene and 35 parts of heavy calcium carbonate
At 0°C, ethylene-vinyl acetate copolymer (C) (melting point 108°C) was injected into one die using an extruder and 18% by weight using another extruder.
It was fed to the die at 0°C, coextruded, and cooled to 80°C to form a two-layer film ((A)/(c) with a thickness of 40°C).
00 tt/100 um) was obtained.

Next, after embossing lOO line dots (depth 50t1m) on this (C) side film,
Reheated to C, stretched 7 times in the longitudinal direction and 6.5 times in the transverse direction, corona discharge treated on the A side, and slit to a wall thickness of 1.
A stretched film of 20 μm was obtained. This stretched film (
The smoothness of the surface on the C) side is 350 seconds, and the average surface roughness (Ra
) was 0.7 μm.

This was processed to obtain a fan-shaped blank for a differential pressure molded cup having a bottom plate diameter of 53 mm and a peripheral wall height of 28 cm.

After fixing this blank in the cavity of the lower female mold of the pressure-air vacuum mold with the printing side in contact with the cavity surface of the mold, the melted polypropylene sheet (approximately 200°C)
5 of the lower female mold using a compressed air vacuum forming machine manufactured by Uniku.
C1m upward, and the pressure is reduced through the vacuum hole at the bottom of the lower female mold, and the blank is adsorbed to the inner surface of the mold.
/cm"G compressed air was supplied from the air supply port side of the upper mold to press the polypropylene sheet to the inner surface of the mold, perform plug assist molding in 10 seconds, and trim to an average wall thickness of 55.
A container mainly made of cup-shaped polypropylene decorated with a blank having a diameter of 0 to 600 μm was molded.

In the containers manufactured in this manner, there was no fading of the print on the blank, and no deformation of the blank was observed. Furthermore, the adhesive strength between the cup-shaped container body and the blank was strong, and the blank could not be peeled off by hand.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the label, Fig. 2 is a plan view of the label seen from the back side, Fig. 3 is a cross-sectional view of the embossed multilayer structure film before stretching, and Fig. 4 is a cross-sectional view of the embossed multilayer film before stretching. It is a partially enlarged view of a layered structure film.

Claims (1)

[Claims] 1) On the back side of the thermoplastic resin film containing inorganic fine powder,
A heat-sealable resin layer having a melting point lower than the melting point of the material resin of the film is provided to form a multilayer structure film, and after embossing the heat-sealable resin layer, the temperature is higher than the melting point of the heat-sealable resin. A method for producing synthetic paper for labels, which comprises stretching a multilayer film at a temperature lower than the melting point of a thermoplastic resin containing fine inorganic powder.