JPS6325026A - Hot-melt adhesive for easily openable shrink packaging body - Google Patents

Abstract

PURPOSE:To obtain an adhesive agent, capable of being coated under a temperature, not exceeding the melting point of synthetic fiber, good in adhesive properties, developing a good bonding force in a low temperature and allowing the shrinkage of a tear tape itself, by a method wherein a viscosity, a softening point, an open time and a set time in a specified temperature are specified respectively. CONSTITUTION:The title adhesive agent is a hot-melt adhesive for shrink packaging body, provided with the viscosity of 100-20,000cps at 150 deg.C, the softening point of 65-120 deg.C and the open time and the set time are 0.5-10sec. When the adhesive is provided with the viscosity of up to 100cps, the adhesive is easily removed and bonding can not be effected when it is bonded to a shrink film by heating, however, when the viscosity exceeds 20,000cps, the processing of a thread becomes difficult. When the softening point is up to 65 deg.C, the adhesive is softened and the shrink thread is easily detached upon heating, however, when it exceeds 120 deg.C, the shrinkage of the shrink film is caused upon bonding a tear tape by heating. When the open time is up to 0.5sec, the curing of the adhesive is too fast, however, when it exceeds 10sec, the curing of the adhesive is too slow and the non-cured adhesive is adhered to an unnecessary part. When the set time is up to 0.5sec, insufficient bonding is caused and, on the contrary, when it exceeds 10sec, a bonding force becomes insufficient after bonding it to the film by pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention is directed to packaging bodies (hereinafter referred to as "
The present invention relates to an adhesive used in a shrink package (hereinafter referred to as "shrink package"), and particularly relates to a hot melt adhesive for adhering a tear strip incorporated inside the shrink package to a film before shrinking.

[Conventional technology and its problems] Synthetic resin film with heat shrinkability (hereinafter referred to as "
It is widely used to package products individually or collectively into units for sale or transportation using shrink film. The package obtained in this way is
In addition to excellent transparency and cosmetic properties, it also ensures the virginity of the product, so it is used as a highly safe packaging that gives consumers a sense of trust, especially in the packaging fields of foods such as confectionery and instant ramen, as well as pharmaceuticals. It is becoming more and more important.

However, in the above-mentioned shrink package, since the shrink film is in close contact with the outer circumferential surface of the packaged item (commodity) under tension, there is a problem in that it is difficult to tear the shrink film on the surface when opening the package. Therefore, in order to eliminate this inconvenience, conventionally, the shrink package has been provided with an easy-open opening means having the following configuration. Namely, ■ a method in which a perforation line is formed in advance on the film surface, ■ a method in which a notch (cut groove) is made in the package film after shrinkage, and a tear ribbon is adhered thereon; The method described above was used to attach a shrinkable cant tape to the inner surface of the film. Each of the above means has its own problems, and in order to solve these problems, one of the inventors of the present invention previously proposed an invention in Japanese Patent Application No. 158383/1983 entitled "Easy-to-open shrink packaging and its manufacturing method." proposed. Hereinafter, the content of the prior invention will be briefly described. This invention provides that the inner surface of a heat-shrinkable film does not shrink even when heated at the shrinking temperature, and that the shrinkage force of the film is applied only when the film shrinks by heating. In other words, as the shrink film shrinks, the opening strip shrinks in length in the longitudinal direction and its thickness also loosens in the radial direction. It is characterized by the fact that it has been installed. The present invention aims to obtain the most suitable adhesive for use in attaching the opening strip to the film, but it can also be used as an adhesive when carrying out the method (2) above.

By the way, as is clear from the above explanation, regardless of the type of tear strip, when arranging this kind of tear strip on the inner surface of a shrink package, it is necessary to unseal the film before heat shrinking. It was necessary to attach the strips, and the adhesive used for this attachment and its usage were generally as follows. The most commonly used
A so-called pressure-sensitive adhesive that is sticky at room temperature is applied to the opening strip in advance and then pressure-bonded to the film surface. This requires separate manufacturing equipment from the above-mentioned bonding process. That is, first, an adhesive is applied to one side of a wide sheet of opening collection material and a release agent is applied to the other side, and then this is wound into a roll, and this time, this roll is passed through a slitter. It had to be cut into thin strips to make opening strips. Another known method is to apply a heat-sealing adhesive to one side of the opening strip and then heat and melt it to bond the two together. There was a problem in that the original shrinkage effect could not be produced in that part because the part had contracted.

The above-mentioned pressure-sensitive adhesive also acts on the contents to be packaged, so careful attention is required when applying it. There was a restriction that it had to be done.

[Summary of the Invention] The present invention is applied to the above-mentioned cut tape in a shrink package as well as the shrink thread for opening in place of the above-mentioned cut tape, which was newly developed by one of the inventors. A new hot-melt adhesive that does not shrink or change in quality during application, and can be easily fluidized and applied to film immediately by heating just before adhering to the unshrinked film. It is one pint of the agent.

The adhesive of the present invention satisfies all of the following conditions specific to shrink packaging.

A. It has fluidity at a temperature that does not alter the properties of the opening strip itself. In other words, even when applied to a opening strip that has heat-shrinkable properties, the opening strip does not shrink. In the case of synthetic fibers, it can be applied at a temperature that does not exceed the melting point of the synthetic fibers.

B. It has good adhesion resistance to the enclosed strip and solidifies immediately when cooled to room temperature.

C. It is possible to heat bond the film and exhibit adhesive strength at a temperature lower than the shrinkage temperature of the film.

D. When the film is introduced into a heated atmosphere furnace for shrinkage and is shrunk, the tear strip with the adhesive still attached will shrink due to the shrinkage stress of the film, or the tear strip will be separated from the film separately. Loosening of the bond to an extent that allows for its own shrinkage.

The present invention aims to provide a hot melt adhesive that can satisfy the above conditions.

[Means for solving the problems] The composition of the adhesive of the present invention has a viscosity of 100 at 150°C.
This hot melt adhesive for shrink packaging has a softening point of ~20.000 cps, a softening point of 65 to 120°C, and an open time and set time of 0.5 to 10 seconds.

Before specifically explaining the structure of the adhesive of the present invention, a general shrink package to which the adhesive of the present invention is applied and a method for making the same will be briefly explained.

Reference numeral 1 in FIG. 1 indicates an example of a shrink package. Similarly, the reference numeral 2 indicates a shrink film, which wraps the entire packaged object 3 from its periphery in a shrunk state.

In the illustrated example, a tear strip 4 is adhered to the inner surface of the film 2 on the center line extending over the top surface of the packaged object 3.

Reference numeral 5 designates a vertical seal portion that occurs when both edges of a strip-shaped shrink film are center-sealed during shrink wrapping as described later, and 6 designates a horizontal seal portion that occurs at the front and rear of the packaged item. The opening strip 4 is fixed to the shrink film 2 with an adhesive 7, but the thread itself is configured to shrink following the shrink action of the shrink film as described later. preferable.

Proceeding to a concrete example of manufacturing the above-mentioned package, in FIG. 2, reference numeral 2a denotes a roll-up of the shrink film, and a strip-shaped pre-shrink film 2b is pulled out from there. On the other hand, while letting out the shrinkable yarn 4 at the same speed, it is placed on the back side of the strip film 2 (
It is attached to the stone surface (in the figure) with adhesive. The adhesive is coated on the opening strip in advance by roll coating or dipping.

An example of an apparatus for applying the adhesive of the present invention to an opening strip will be explained with reference to FIG. The adhesive 15 is adhered to the surface of the opening strip 4 at intervals of about 3 to 5 mm by a dip roll 17 that rotates in the adhesive melting tank 16 and a serrated transfer roller 18 that rotates in contact with the roller. I'm going to go.

In the figure, the symbol @7 is a pressure roller, the symbol 8 is a receiving roller, and the symbol 19 is a guide roller. The amount of adhesive applied to the opening strip is 40 to 150% of one opening of the opening strip, preferably 6
It is 0-100%.

As described above, adhesive is applied in advance to the opening strip 4 shown in FIG. ) is continuously glued so that it is located at The strip-shaped film with thread is then led to a folder 9, where it is wrapped around the packaged object 3 and then center-sealed into a tube shape through a seeker 10 with both sides of the film overlapped. be done. Reference numeral 11 denotes a carry belt, and a position control device 712 built into it.
This controls the transport speed of the package and synchronizes it with the fusing sheep 13 at the subsequent stage. In addition, carry belt 1
1, the continuous film part is cut and horizontally sealed together with the film 2 by a melt-cutting sheet 13, and becomes an independent package 1 before shrinking. The individualized packaging bodies 1 are introduced into a heating atmosphere furnace 14, and the shrink film 2 is heated to 140 to 180°C in this furnace. A shrink package 1 as a product is formed.

The hot melt adhesive for shrink packaging of the present invention has the following properties in the structure of the shrink packaging as explained in H below.
It is used as an adhesive for opening strips to be adhered to shrink films as opening strips for shrink packages.

In the above explanation, the adhesive of the present invention is attached to the opening strip,
Although a series of steps for use in a shrink packaging machine has been described, if a roll of tear strips to which adhesive is attached is manufactured and left at 0C, it can be used in any packaging machine at any time.

With the composition of the adhesive of the present invention, the viscosity at 150°C is 10
0 to 20,000 CI)S, preferably 1,000 to
The reason for setting the viscosity to 10.000 cps is that if the viscosity is less than 10.000 cps, when it is heat-adhered to a shrink film using a packaging machine or heat, it will easily come off even after it has been adhered, and the adhesion will not be possible. This is because if the value exceeds ooocps, it becomes difficult to process the yarn.

In addition, the softening point was set at 65 to 120°C because if the softening point is lower than 65°C, when the package is heated in a heated atmosphere furnace, the adhesive of the shrinkable thread will soften and the shrinkable thread will easily come off, whereas if it exceeds 120°C, it will shrink. This is because there is a risk that the shrink film may shrink when the opening strip is heat-bonded to the film via an adhesive.

Furthermore, both open time and set time are 0.5 ~
It is necessary to set the time to 10 seconds.

Here, open time means the time during which hot melt adhesive can be bonded at a constant temperature when heated to soften and melt and adhere to a film, and open time is 0.
．． If it takes less than 5 seconds, the adhesive will harden too quickly and the adhesion will not be successful. If it takes more than 10 seconds, the adhesive will harden too slowly, causing problems such as unhardened adhesive adhering to unnecessary areas. This is not desirable because it causes

In addition, set time means the time from adhesion until the adhesive completely hardens and adheres, and set time is 0.
If the time is less than 5 seconds, insufficient adhesion may occur, whereas if the time exceeds 10 seconds, the thread may come off due to insufficient adhesive force after being pressed onto the film.

The method for measuring open time and set time is as follows.

Open time measurement method Heat-melted hot-melt adhesive was applied to the surface of a plastic plate using a hot-melt gun for approximately 297TrL.
After applying 2 in a linear manner, immediately apply 30 mm vertically and horizontally on the linear adhesive.
Press and peel off the pasted paper, repeat the same operation every second, and measure the time until the paper can be peeled off without tearing, and use it as the open time.

Set time measurement method: Cut double-sided cardboard to 25m + width x 100s +, apply molten hot melt adhesive to one end, fold the cardboard in half, overlap the other end with the adhesive area and press. This process is repeated every second, and the set time is defined as the time it takes for the stacked cardboard to adhere to the area where the adhesive has been applied and no longer spring up.

Among thermoplastic resins, those generally known as hot-melt adhesives can be applied to the present invention as hot-melt adhesives that satisfy the above constitution of the hot-melt adhesive for shrink packaging of the present invention. Preferred examples include polymers whose main component is ethylene/vinyl acetate copolymer (EVA), ethylene/edyl acrylate copolymer (EEA), modified copolymers thereof, olefin polymers, etc. It is a hot melt adhesive. The selection and blending ratio of these polymers are determined so that they fall within the respective ranges of viscosity, softening point, open time, and set time defined in the present invention, and also depend on the materials of the shrink yarn and shrink film to be bonded. It is preferable to adjust the composition of the components as appropriate.

As the shrink film to which the adhesive of the present invention is applied, polyethylene, polypropylene, polyester, polyvinyl chloride, etc., which are generally known as shrink films, can be used.

In addition, the threads and tapes used as opening strips of the shrink package include various single yarns, plied and twisted yarns made of natural fibers, synthetic M fibers, semi-synthetic TIII fibers, or regenerated fibers previously applied by one of the present inventors. The adhesive of the present invention can be applied to known cut tapes as well as shrinkable threads that shrink following the shrinkage of the film.

This will be specifically explained below using examples.

[Example] 20 parts of paraffin and wax with a melting point of 58°C made by vA, M118,
A hot melt adhesive consisting of 40 parts of EVA resin with a vinyl acetate (V^) content of 28% and 40 parts of ester gum with a softening point of 82 to 92°C was prepared, and its softening point, open time,
Table 2 shows the results of measuring set time and viscosity.

Manufacture of opening strips for shrink packages Polyester (polyethylene terephthalate) is used as a raw material and melt-spun into 30 fiber bundles through a spinning nozzle, and each single fiber has a thickness of 3 denier. Twist the fiber bundle 800 times on each side! j
Yes, it is crimped. When two bundles are twisted together after crimping, 60 single fibers are combined, and polyester J is twisted 133 times per meter. A rough shrinkage thread was obtained.

Coating the adhesive onto the opening strip is carried out using the adhesive coating device shown in FIG. 3. The adhesive is applied from the adhesive melting tank obtained above using a dip roll and a transfer roller onto the surface of the shrinkable yarn obtained above at intervals of approximately 3 to 5 square meters, so that the amount of adhesive applied is one coat of the yarn. The amount of adhesion is approximately 80%.

Manufacturing Test for Shrink Packaging Using the shrink yarn to which the adhesive obtained above was adhered, a manufacturing test for shrink packaging was conducted using the standard packaging method described in FIG. 2.

A polypropylene film with a thickness of 15 μm was used as the shrink film, and as explained in FIG. Continuously heat and bond to the underside of the film before shrinking.

Thereafter, while overlapping the packaged object, the strip-shaped film is center-sealed by a vertical sealer, and then laterally sealed and cut along the cut line L by a welding sheet to form individualized packages. The shrink film was introduced into a heating atmosphere furnace and heated at 150 to 160°C to obtain a shrink package as a product.

This shrink packaging! The suitability of the adhesive for J construction was evaluated by the following method.

The shrinkable thread was passed through a melting tank with a coating temperature of 140 ± 5°C, which was suitable for coating on unsealed strips, and passed through the gap between ironing plates made of hard rubber with a spacing of 0 to 0.2 m between the rubber plates, at a pulling speed of 100 m/min. The state of pulling up, adhesive assimilation, winding, running suitability, etc. were visually judged and evaluated.

◎: Excellent O: Good Δ: Slightly poor X: Defective adhesion suitability on the packaging machine On the shrink packaging machine, the opening strip is adhered to the surface of the unshrinkable film, the item to be packaged is wrapped, and the shrink package is formed. The slipperiness of the thread and the state of adhesion to the film were evaluated until it was obtained.

Sliding suitability ◎: Excellent O: Good Δ: Slightly poor X: Adhesion to defective film ◎: Opening strip is firmly adhered in a straight line o: gi
I The sealing strip is firmly glued in a substantially straight line Δ: The unsealing strip is glued with some bends. After leaving the shrink package from the heating atmosphere furnace, the package is torn open without affecting the part to which the tear strip is attached, and the tear strip is attached to the film and the tear strip is attached to the film. Peel it off more gently and check the peel resistance.

◎: Excellent O: Good ∆: Slightly poor X: Poor Shrinkage state of opening after heating the shrink film After heating the shrink film, the shrinkage state of the opening strip of the cooled shrink package is visually judged and evaluated.

◎: The unsealing strip has shrunk in a straight line without any slack. ○: The unsealing strip has shrunk almost without sag. △: The unsealing strip has contracted somewhat insufficiently and is slightly sagging. X: The unsealing strip has not contracted enough. The results of evaluating the suitability of the adhesive for coating on the opening strip, the adhesion suitability on the packaging machine, the adhesive strength when heated in a heating atmosphere oven, and the state of shrinkage of the opening strip after heating the Sealink film were evaluated. It is shown in Table 2.

Examples 2 to 4, Comparative Examples 1 to 4 Hot melt adhesives were prepared in the same manner as in Example 1 using the chemical formulations shown in Table 1, and shrinkable threads as opening strips were also produced in the same manner as in Example 1. Then, a manufacturing test of the shrink package was conducted in the same manner as in Example 1, and the adhesion suitability of the adhesive to the opening strip, the adhesion suitability of the packaging machine and H, the adhesive strength when heated in a heating atmosphere furnace, and the shrink film after heating were evaluated. Table 2 shows the results of evaluating the yield and line condition of the unsealed yarn.

(Left below) According to the results in Table 2, Examples 1 to 4 had a viscosity of 100 to 20,000 cps at 150°C and a softening point of 65 to 1.
201 Open time and set time are both 0.5
When the hot melt adhesive for shrink packaging of the present invention, which is within the range of ~10 seconds, is used in the production of shrink packaging, the adhesive's coating suitability for opening threads, packaging suitability, adhesive strength when heated in a heating atmosphere furnace, In all the shrinkage states of the opening thread after heating the shrink film, the viscosity, softening point,
This is superior to the results of Comparative Examples 1 to 4, which used adhesives whose open time and set time were outside the range.

[Effects of the Invention] Therefore, the adhesive of the present invention can be used to manufacture shrink packages. Since the opening string can be shrunk without the solidified adhesive preventing it from shrinking, a beautiful shrink package can be obtained.

(2) 1 when gluing the opening thread to the shrink film
007FL / Since heat bonding is possible at a speed above fiber separation and can be bonded at a temperature lower than the shrinkage temperature of the film, the film will not shrink and the unsealing thread can be bonded to the film, and as described in (1) above. Coupled with this action, the opening thread can be neatly and reliably adhered to a predetermined position on the inner surface of the shrink package.

(3) Since the J3 opening thread on the shrink packaging machine has good sliding and running properties, the packaging machine has excellent operability.

(4) Coating suitability when adhesive is applied to the opening thread in advance, good adhesion between the opening thread and the film in the shrink packaging machine, solidification at room temperature, open time, set time, viscosity By setting the value within a predetermined range, there are no problems such as adhesion of the adhesive to other parts, and workability is good, making it suitable for the shrinkable yarn of the inventor's earlier application, as well as general cut tape, etc. It is excellent as an adhesive for opening strings for shrink packaging.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a shrink package to which the adhesive of the present invention can be applied, and FIG. 2 is a perspective view showing an example of the outline of a shrink package manufacturing apparatus to which the adhesive of the present invention can be applied. FIG. 3 is an explanatory diagram of an apparatus for applying the adhesive of the present invention to an opening strip. DESCRIPTION OF SYMBOLS 1... Shrink package, 2... Shrink film, 3... Item to be packaged, 4... Opening strip, 5... Vertical seal, 6... Horizontal seal, 7... Crimping [ ”-La, 8・
...Receiving roller, 9...Folder, 10...Vertical sealer, 11...Carry belt, 12...Position control device, 13...Welding area sealer, 14...Heating atmosphere electric furnace, 15... Adhesive, 16... Melting tank, 17...
Dip roll, 18...Transfer roller, 19
...Guidance roller. Applicant: Honshu Paper Co., Ltd. (Douichikoku) Agent: Ashi 1) Naoe Figure 3

Claims (1)

[Claims] 1 Viscosity at 150℃ 100-20,000cps
A hot melt adhesive for shrink packaging, characterized in that it has a softening point of 65 to 120°C and an open time and set time of 0.5 to 10 seconds.