JPS6020984A - Heat bonding film for sealant - Google Patents

Abstract

PURPOSE:To provide a heat bonding film for sealant having a sealant layer consisting of a specified base layer with corona discharge treated surface and a specified hot-melt resin, which can be dry laminated and has easy openability. CONSTITUTION:The film has a base layer 1 consisting mainly of ethylene polymer and a sealant layer 2 consisting of ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer, ethylene/acrylic ester copolymer or a mixt. thereof which may contain, when necessary, at least one additive such as adhesion improver, lubricant, blocking inhibitor or heat stabilizer. The layer 1 contains 3- 50wt% hot-melt resin and is corona discharge treated on the surface. It can be bonded with paste or sandwiched with polyethylene, has easy openability and is useful mainly as cover for plastic container for food packaging.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a thermal adhesive film for sealant suitable for lid materials of plastic containers. More specifically, the present invention relates to a heat-adhesive film for a sealant, which is mainly used as a lid material for plastic containers for food packaging, has an easy-to-open property, and can be pasted with glue and can also be pasted with a polyethylene sandwich.

[Background technology]

Conventionally, sealants for lids of plastic containers have often been made of the same material as the container and sealed by heat sealing. However, with this method, the adhesive strength between the container and the lid is too strong, so it is necessary to tear the lid by hand or cut it open with a cutter knife, which poses a problem in terms of the ease of opening the lid. there were.

Various proposals have been made to eliminate such inconveniences. One of them is a method known in Japanese Patent Publication No. 55-35310, which achieves easy opening through the relationship between the glabellar peeling between the base layer of the coextruded film and the sealant layer and the breaking strength of the sealant layer. However, the peel strength when opened is weak at 200 g/15 mm width, and there is a risk that the package may easily open due to impact during transportation.

On the other hand, one method that has recently become common is to coat the inner surface of the lid material with a hot melt resin suitable for the plastic container in question. In addition, a method in which a single film made from hot-melt resin is sandwich-laminated with a base film and polyethylene resin has come to be seen here and there. However, both methods have the following problems in workability, practicality, etc., and a solution to these problems has been desperately needed. That is, the coating type has large variations in seal peel strength and is unstable, and is also inferior in heat resistance during boiling. Furthermore, a large amount of low molecular weight substances are extracted by n-hebutane, which poses a hygiene problem. Therefore, attempts have been made to improve the coating type in order to solve these problems, but new problems have arisen, such as the viscosity becoming too high, making it difficult to coat, and a satisfactory result has not been obtained.

Improvements have been made by extrusion lamination of hot-melt resins, but in the case of low-volume production of multi-living species, there is a lot of loss and costs are high.

On the other hand, hot melt resin single film polyethylene
In the case of sandwich laminated products, the single film is not stiff and the flatness is poor due to walnuts caused by the uneven thickness of the film, causing problems in processing suitability. In this case, as in the case of hot-melt resin extrusion laminate, there is a lot of loss when producing a wide variety of products in small quantities, resulting in high costs and disadvantages in terms of delivery time.

Characteristics required for lid materials include printing pitch accuracy and curling properties after lamination with the printed base material, but conventional products still have many problems with these points. .

When the lid base material is paper, there is also a problem of poor opening properties due to film breakage in the sealant part, and damage to the printed part due to oil penetration.

[Purpose of the invention]

In view of the above-mentioned circumstances, an object of the present invention is to provide a heat-adhesive film for a sealant that does not have these disadvantages and can be dry laminated and has easy opening properties.

[Disclosure of the invention]

In order to achieve such an object, the present invention includes a base layer consisting essentially of an ethylene polymer and a sealant layer consisting of a hot melt resin selected from the following resin group, and the base layer is The hot melt resin is 3~
The gist of the film is a thermal adhesive film for a sealant, which contains 50% by weight and is characterized in that the surface of the base layer is subjected to a corona discharge treatment.

Hot melt resin group; ethylene/vinyl acetate copolymer,
Ethylene/acrylic acid copolymer, ethylene/acrylic acid ester copolymer, or other ethylene copolymer alone or in a mixture, and adhesion modifiers, lubricants, antiblocking agents, heat stabilizers, etc. as necessary. There are few additives (
It is a combination of both.

Hereinafter, one embodiment of the present invention will be described in detail based on the accompanying drawings.

FIG. 1 is a cross-sectional view of a model of a thermal adhesive film for sealant according to the present invention. The first layer is the base M1,
This is a resin layer whose main component is essentially an ethylene polymer, which is selected depending on the intended use.

The second layer is a sealant layer 2, which is made of an extrudable hot-melt resin that is compatible with the material of the target plastic container. Here, the ratio of the thickness of each layer can be adjusted as appropriate based on suitability for lamination, stable adhesion to the material to be bonded, economical efficiency, and other required properties. Incidentally, the surface 3 of the base layer 1 is subjected to corona discharge treatment to enable dry lamination. As shown in FIG. 1, the heat-adhesive film for sealant according to the present invention is required to have at least two layers: a base layer 1 and a sealant layer 2 overlaid thereon. These two layers 1, 2 are generally superimposed by known coextrusion methods.

The resin component of the sealant layer 2 is ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer, ethylene/acrylic acid ester copolymer, or other ethylene copolymer alone or in a mixture thereof. The sealant layer may be composed of such a resin alone, but usually contains at least one additive such as an adhesion modifier, a lubricant, an antiblocking agent, a heat stabilizer, etc. as necessary. It is blended with this resin component. The sealant layer contains the above-mentioned resin as the main component (97 to 70% by weight), and adhesion modifiers (hydrogenated rosin, rosin resin, terpene resin, 9 petroleum resins, coumaron/inden).・Contains 3 to 30% by weight of styrene resin, isoprene resin, etc.), and also contains lubricants, anti-blocking agents (fatty acid esters, amides, amines, inorganic compounds, etc.) and heat stabilizers (
Butylated hydroxytoluene, tocopherol iL n
-octadecyl-β(4'-hydroxy 3', 5'
-di-t-butylphenyl)propionate, 414'
-butylidenebis(4-methyl-6-t-butylphenol), 1.3.5-)limethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tetrakis [ Methylene-3-(3',
5'-di-t-butyl-4'-hydroxyphenyl)
Additives such as propionate comethane, etc.)
Preferably, a hot melt resin that can be extruded and formed into a film in an amount of 50 to 5000 ppm is selected as the main component, and 10 to 30% by weight of an adhesion imparting modifier is selected as the main component. and 500 to 2000 ppm each of lubricants, antiblocking agents, and stabilizers.
More preferred is a formulation in which both of these components are blended. The thickness of the sealant layer is preferably 5 to 25 microns.

The ethylene polymer that is the main component of the base layer 1 includes medium-low pressure polyethylene and low-density polyethylene such as high-density polyethylene and medium-density polyethylene, as well as copolymer component blending ratios such as straight-line low-density polyethylene. It also includes ethylene copolymers that can be considered to be essentially ethylene polymers because of their low content.

The base layer is required to be stiffer within a certain range compared to the sealant layer 2. The range of the strength is preferably a range in which the Young's modulus is 1.5 to 10.0 times that of the sealant layer, and a range in which the Young's modulus is 4.0 to 7.0 times is particularly preferred. . In order to impart such a puffer ratio to the base layer, it is preferable to select polyethylene as the main component of the base layer. In particular, the density is 0.93
It is preferable to select a single type of polyethylene or a mixture of multiple types of polyethylene within the range of 0.960 and a melt index of 2 to 2o.

It is necessary that the base layer 1 contains 3 to 50% by weight of the aforementioned resin constituting the sealant layer 2.

This makes the adhesive force between the sealant layer and the base layer suitably strong. This is essential to maintain the original functions of the sealant layer, such as easy opening, even if polyethylene resin is used for the sealing part of the target container.

Easy-opening here refers to the fact that a general consumer can easily open a container by simply grasping the edge of the lid with their fingers and pulling it off without using any other tools. means. For this purpose, interfacial peeling must occur at the heat-sealed interface between the container seal and the lid. On the other hand, the sealant must have sufficient sealing strength between the filled container and the lid material to withstand various shocks and external pressures received immediately before use, such as shocks received during transportation.

Taking these points into consideration, it is generally said that the peel strength of a sealant for a container lid material is about 500 to 1200 g/15 mm width. Therefore, also in this invention,
The interlayer adhesion between the base layer of the coextruded film and the sealant layer is required to be at least 1200 g/15 mm or more.

In order to keep the sealing strength of the sealant layer constant at all times, distortion should not occur between the sealant layer and the base layer. This is because if distortion occurs in this portion, the accompanying internal stress will cause a decrease in seal strength. For this reason as well, it is necessary that the base layer contains a resin having the same composition as the sealant layer. In addition, here, the resin having the same structure as the sheet tent layer does not necessarily mean that it is the same resin as the resin currently used for the sealant layer. In other words,
A hot melt resin selected from the above hot melt resin group (ethylene/vinyl acetate copolymer, ethylene/acrylic acid copolymer, ethylene/acrylic acid ester copolymer, or other ethylene copolymer alone or mixture) The resin may be different from the resin currently used for the sealant layer as long as it is.

In order to obtain the various effects described above, it is necessary that the base layer contains 3% by weight or more of the resin for forming the sealant layer. However, if the content exceeds 50% by weight, the stiffness becomes too weak, causing a problem in the suitability for processing as a film. Therefore, the resin content for forming the sealant layer is 3 to 3.
It is necessary to set the content to 50% by weight. Preferably 7~
It is 30% by weight.

Easy-open lid materials for plastic containers for food packaging (including combinations of plastic and paper) are made of various base materials (such as special paper, aluminum foil, stretched polyester film, and other stretched plastic films). It is finished by laminating the thermal adhesive film for an easy-open sealant according to the invention. The above-mentioned bonding method includes a polyethylene sandwich lamination method and a dry lamination method, but it is preferable to adopt the dry lamination method in order to take advantage of the effects of the present invention described above. Taking this into consideration, in the present invention, the base layer surface 3
For example, if the wetting tension is 37 to 47 dyn/
Corona discharge treatment is performed by a known method so that cffI is obtained. By doing so, adhesion using a dry laminating adhesive becomes possible.

Here, referring to the plastic container for food packaging which is the subject of the lid material using the thermal adhesive film for easy-open sealant according to the present invention, the container body is made of polyethylene resin, polypropylene resin, polyvinyl chloride resin. Molded products obtained by injection molding/blow molding using materials such as polystyrene resin, nylon resin, polyethylene terephthalate resin, acrylonitrile modified resin, ethylene/vinyl alcohol copolymer resin, ionomer resin, etc.
(including composite/foamed products), single-sheet composite coextruded sheets, or aged sheets made from multilayer laminated sheets, but also includes those in which paper, aluminum foil, or steel plates are partially used. The materials used for the sealing part of the target container are polypropylene resin and polystyrene resin in order to increase the degree of freedom in selecting the hot melt resin that makes up the sealant layer.

Polyethylene resin and polyvinyl chloride resin are preferred.

Common examples of plastic products covered by this invention include polypropylene molded trays, polypropylene molded cups, polypropylene/ethylene vinyl alcohol copolymer/polypropylene composite molded products, polystyrene molded products 1-foam polystyrene cups, and foamed bottles. , a styrene tray, a vinyl chloride molded product, a medium-low pressure polyethylene cup molded product, and deep-draw thermoformed products of various configurations.The present invention will be specifically explained below with reference to Examples.

(Example 1) Samples No. 1 to No. 5 were prepared. The thickness of the base layer was 20 μm in each case, and the resin used was selected as follows. That is, No. 1 has a specific gravity of 0.9. A polypropylene resin with a melt index (hereinafter abbreviated as rMIJ) of 7 is used, and No. 2 is a specific gravity of 0.94. Old 9 medium and low pressure polyethylene resin, No. 3 has a specific gravity of 0.94. No. 4 is a mixture of 90% by weight of MI9 medium-low pressure polyethylene resin and 10% by weight of ethylene-vinyl acetate copolymer-based hot melt resin, with a specific gravity of 0.94. A mixture of 50% by weight of MI9 medium and low pressure polyethylene resin and 50% by weight of ethylene/hinyl acetate copolymer-based hot melt resin, and No. 5 has a specific gravity of 0.94 and 30% by weight of MI9 medium and low pressure polyethylene resin. % and 70% by weight of an ethylene/vinyl acetate copolymer-based hot melt resin was selected.

A sealant layer made of an ethylene/vinyl acetate copolymer-based hot melt resin (specific gravity 0.93. MI8) was superimposed on the base layer to a thickness of 20 μm.
Sample thermal adhesive films for easy-to-open sealants were prepared by coextrusion using a composite T-die method and in-line corona discharge treatment to a wetting tension of 45 dyn/cm.

Each sample was finished into a lid material by dry laminating so that it had a composition of 20μ stretched polyester film/9μ aluminum foil/40μ trial film.

In addition to examining the Young's modulus of each film obtained as a sample, we also examined its suitability for dry lamination. moreover,
The adhesion between each of the lid materials obtained as described above and the following barrier containers was examined by peel strength and gas filling tests. Here, the barrier container is a container molded from a material consisting of 150 μm of vinyl chloride resin, 20 μm of ethylene polyvinyl alcohol resin, and 8 μm of polypropylene resin.
It is a container with dimensions of 0°25 x 80 x 120 x 30 mm.

Young's modulus is determined using Tensilon at a tensile speed of 30+nm.
/min, 20°C, 65% R)l. In the gas filling test, CO2 gas was filled using an automatic filling search machine FV603 manufactured by Jinbun Kikai, and the sealing conditions were 150.
It was examined after being left at 5°C for 7 days at 1 second at 5°C.

Peel strength was measured using Tensilon at a tensile rate of 2001/
The test was conducted under the following conditions: 1.90" peeling at 20° C., 65% R).

The results are shown in Table 1, and the superiority of the easily openable sealant thermal adhesive film according to the present invention was confirmed.

(Margins below) Table 1 (Example 2) By prototyping samples with various thickness ratios of the base layer and sealant layer in the resin composition of samples No. 3 in Example 1, and conducting various evaluations. , the results shown in Table 2 were obtained.

In the evaluation shown in Table 2, the Young's modulus of the film was measured under the same conditions as in Table 1. The lid material used to evaluate the peel strength with the PP sheet, printing pitch property, curling property of the lid material, and oil resistance was dry laminated to have a composition of 20μ stretched polyester film/9μ aluminum foil/40μ trial film. It is obtained by processing. Note that the thickness of the PP sheet is 0.
．． It is 25mm. Peel strength with PP sheet is
Measurement was carried out under the same conditions as in Example 1 using Tensilon, which was sealed at scale 8 using Fuji Impulse Sealer FG400. The oil resistance of the lid material was evaluated using salad oil at 100° C. for 5 minutes.

From this result, a criterion for determining the influence of the thickness structure of the easily openable sealant thermal adhesive film of the present invention on practicality was obtained. In other words, this table suggests the possibility of selecting the thickness structure in accordance with the required characteristics.

(Margins below) Table 2 (Example 3) The practicality of the foamed polystyrene cups and lid materials having various configurations shown in Table 3 was evaluated.

In this evaluation, the openness was determined under sealing conditions: 150°C x 2
Judgment was made based on the presence or absence of paper tear at 5 kg x 0.5 seconds. Oil resistance evaluation was carried out using salad oil at 40°C x 24
It was done under the time constraints. For workability, the quality of the bonding process was visually determined. Curling property was determined on a disc-shaped cut product of 100IIllIφ, and i-viability was determined by an n-hebutane extraction test.

As a result, it was confirmed that the lid material obtained by dry laminating the thermal adhesive film for easy-open sealant according to the present invention (the film of Sample No. 3 in Example 1) was comprehensively superior. (Margins below) Table 3 [Effects of the Invention] The thermal adhesive film for easy-open sealants according to the present invention has the above-described structure5, and can be used as a sealant for lids of plastic containers. Since dry lamination is also possible, it is advantageous in terms of loss prevention and delivery deadlines in the case of high-mix, low-volume production.In addition, extrusion lamination can prevent unstable printing pitch accuracy, prevent curling, and improve oil resistance and hygiene. It is advantageous in terms of improvement, and it also has the advantage of being cheaper than a single film made of hot melt resin.

Therefore, the thermal adhesive film for an easy-open sealant according to the present invention takes advantage of these characteristics to be used in plastic containers for lactic acid bacteria drinks, plastic containers for dessert foods, containers for cup portions, containers for tofu, and other various containers. It is extremely effective when used.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a model showing an embodiment of the easily openable heat-adhesive film for sealant according to the present invention. l...Base layer 2...Sealant N3...Base layer surface agent Patent attorney Takehiko Matsumoto

Claims (1)

[Scope of Claims] +1) A base layer consisting essentially of an ethylene polymer and a sealant layer consisting of a hot melt resin selected from the following resin group, the base layer containing the hot melt resin. 1. A thermal adhesive film for a sealant, characterized in that the film contains 3 to 50% by weight of the following, and the surface of the base layer is subjected to corona discharge treatment. Hot melt resin group; ethylene/vinyl acetate copolymer,
Ethylene/acrylic acid copolymer, ethylene/acrylic acid ester copolymer, and other ethylene copolymers alone or in mixture, optionally containing adhesion modifiers, adhesive agents, antiblocking agents, and heat stabilizers. It is made by mixing at least one kind of additives such as additives.