JPH11320741A - Gas barrier multilayer heat sealing film and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas barrier multilayer heat sealing film having stable film forming suitability, excellent gas barrier properties, and heat sealability in a co-extruded multilayer film containing a gas barrier layer and a method for manufacturing it. SOLUTION: A barrier co-extruded multilayer film 10 comprises a heat sealing (HS) layer 5 having a density of at least 0.900 to 0.920 g/cm<3> and made of a linear polyethylene, a cushion layer 4 made of a plastomer having a density of 0.880 to 0/cm<3> , an adhesive resin layer 21, a gas barrier layer 3 having an ethylene content of 25 to 50 mol.% and occupying the EVOH of a saponification rate of 90% or more in 50 wt.% or more of the entirety, an adhesive resin layer 22 and a sticky layer 1 made of a low-density polyethylene for occupying 10% or more of the entirety in thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a barrier film formed from a plastic film, and in a bag film capable of heat sealing, a saponified ethylene / vinyl acetate copolymer (hereinafter referred to as EVOH) constituting a gas barrier layer for oxygen or the like. A multi-layer co-extruded film having excellent bending resistance using a gas-barrier multilayer heat-sealing film (hereinafter, referred to as a barrier multilayer HS film), a method for producing the same, and a bag using the same. Belong.

[0002]

2. Description of the Related Art Soft packaging films comprising a plastic film as a base material have been frequently used for bags which are required to have excellent heat sealing properties and to have good sealing properties. A bag having excellent water vapor barrier properties (hereinafter, referred to as moisture-proof properties) and gas barrier properties for oxygen and the like (hereinafter, gas barriers are simply referred to as barriers) absorbs and absorbs moisture through the bags. It has been difficult to avoid deterioration of the contents due to oxidation due to moisture or an active gas such as oxygen. In order to prevent deterioration due to moisture, a multilayer film composed of a stretched plastic film and a heat sealant layer (hereinafter, referred to as an HS layer) of a polyolefin such as polyethylene or polypropylene has been used. And when more excellent moisture-proof properties are required, a film with excellent moisture-proof properties, such as an aluminum foil, a plastic film on which metal aluminum or silicon oxide is deposited, or a laminated film in which a film coated with vinylidene chloride is laminated. Bag was used. And, in the case of the contents whose water content is to be further avoided, a moisture absorbent such as silica or calcium oxide is also enclosed in the bag, which is satisfactory as a bag having moisture proof properties.

When the contents are deteriorated by gas, especially oxygen gas, the above-mentioned polyolefin is used as an HS layer, and a film having excellent barrier properties such as EVO is used as a barrier layer.
H, a modified polyamide, an aluminum foil, a plastic film on which metal aluminum or silicon oxide is vapor-deposited, or a bag body made of a laminated film laminated with a film coated with polyvinyl alcohol or vinylidene chloride has been used. Then, in order to prevent deterioration due to oxygen gas remaining in the bag, "vacuum packaging" from which gas is removed, "gas replacement packaging" in which oxygen is replaced with an inert gas such as carbon dioxide, or oxygen gas is absorbed. The so-called "deoxidizer" is enclosed in a bag and used.

[0004] However, vinylidene chloride constituting the barrier layer is a preferable packaging material due to the risk of air pollution due to chlorine compounds when the packaging material is incinerated and disposed of, because of the problem of the cost of removing pollutants. It cannot be said. In addition, since the laminated body obtained by laminating a plastic film on which aluminum foil, metal aluminum or silicon oxide is deposited is inferior to the plastic film in terms of extensibility, the above-described material has a pinhole at a bent portion or a bent portion. This causes a problem that the barrier property in the initial state cannot be maintained. Further, although a vapor-deposited film is relatively inferior to a pinhole, it is inferior to a plastic film. Accuracy, dimensional stability). Particularly, in a pillow-type gusset bag or a drawstring-shaped packaging bag having a twist portion, there is a problem that pinholes are easily generated in the deposited film.

[0005] Laminated films containing polyvinyl alcohol films exhibit excellent barrier properties when dried,
There is a problem that the pinholes are inferior due to poor bending resistance, and the barrier property is remarkably reduced under the influence of moisture under high humidity. EVOH is a material that is less susceptible to moisture than a polyvinyl alcohol film. However, the oxygen permeability is significantly affected by the copolymerization ratio of ethylene. For example, the oxygen permeability of EVOH at 20 ° C. where the copolymerization ratio of ethylene is 32 mol% is 0.3 to 0.5 cc · 20 μm / m ² · 24.
h · atm, and EVOH having a copolymerization ratio of ethylene of 47 mol% is 4.5 to 5.3 cc · 20 μm / m ^2.
・ 24h ・ atm. Therefore, when EVOH with a low ethylene content, which is a grade having excellent barrier properties, is used, pinholes are generated due to bending and heat / pressure of the heat-sealed portion, similarly to polyvinyl alcohol, and the barrier properties are reduced accordingly. It was difficult to avoid the problem of being easy.

[0006] The above EVOH is a resin which is liable to be thermally decomposed. For example, when a co-extrusion film is formed with another resin by a T-die method, it is decomposed at high temperature to form a carbide or a gel-like substance. Is likely to cause poor appearance, and
The viscosity of the polyethylene used as the HS layer was significantly reduced, and the film formation was not stable. On the other hand, at a low temperature suitable for the workability of the resin of the HS layer, there is a problem in that the resin flow becomes uneven, and streaky thickness unevenness occurs in the flow direction of film formation. Circular die method (inflation method)
In the case of film formation by using
At a processing temperature of 35 ° C., when a multi-layered film using a linear polyethylene (hereinafter, referred to as LLDPE, and a low-density polyethylene is referred to as LDPE) having an excellent heat-sealing property as an HS layer is formed, the melt viscosity becomes low. Insufficiently, the shape of the balloon (tube formed by the molten resin at the time of the film formation of the insulation) fluctuates, so that the thickness and width of the film fluctuate, resulting in a problem of poor film formation. Also, conversely,
At a temperature of 200 ° C. or less, which is suitable for the processing temperature of LLDPE, there is a problem that unevenness occurs in the flow of the resin and streaky thickness unevenness occurs in the flow direction of film formation.

[0007]

SUMMARY OF THE INVENTION According to the present invention, when EVOH, which is excellent in barrier properties but is inferior in bending resistance as a film and has a small ethylene content ratio, is used, bending or heat sealing, particularly folding in a gusset bag or the like, is used. The challenge was to provide a film that produced a "barrier multilayer HS film" that prevented the occurrence of pinholes in the seal portion and the resulting decrease in barrier properties without thermal decomposition during film formation and thickness fluctuations. Is what you do.

[0008]

In order to solve the above problems,
Barrier multilayer HS film of the present invention, HS layer at least density of the LLDPE of 0.900~0.920g / cm ^3, density of 0.880~0.895g / cm ³
Cushion layer consisting of plastomer layer, adhesive resin layer,
Ethylene content 25-50 mol%, saponification rate 90%
The above-mentioned ethylene / vinyl alcohol copolymer is formed by laminating a barrier layer comprising 50% by weight or more, an adhesive resin layer, and a bonding layer comprising a thermoplastic resin. Further, a resin having a melt flow ratio (hereinafter, referred to as MFR) of the resin constituting the HS layer and the bonding layer is a barrier multi-layer HS film smaller than 5 g. Further, the present invention provides a method for producing a barrier multi-layer HS film, wherein the film formation of the barrier multi-layer HS film is performed by a circular die method at a temperature of 235 ° C. or lower.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a barrier multi-layer HS film of the present invention has at least JIS K7122.
6.2 HS layer 5 made of LLDPE having a density of 0.900 to 0.920 g / cm ³ measured according to the B method (pycnometer method), and a density of 0.880 to 0.895 g / c.
cushion layer made of plastomer layer of m ³ 4, the adhesive resin layer 22, an ethylene content of 25 to 50 mol%, saponification of 90% or more of ethylene-vinyl alcohol copolymer multilayer film overall 50 wt% It is formed by laminating the barrier layer 3 including the above, the adhesive resin layer 21, and the bonding layer 1 made of a thermoplastic resin in layer order.
The MFR of the resin constituting the HS layer 5 and the bonding layer 1 measured under the test conditions 4 defined in Table 1 of the JIS K7210A method is a barrier multilayer HS film 10 smaller than 5 g. In addition, when the barrier multi-layer HS film 10 is formed, the melt flow ratios of the innermost HS layer 5 and the outermost bonding layer 1 are both changed.
This is a method for producing a barrier multi-layer HS film composed of a resin smaller than 5 g and performed at a temperature of 235 ° C. or less by a circular dicing method.

[0010] As shown in FIG.
The bonding layer 1 of the S film 10 and the base film 8 or the unprinted base film on which the picture layer 7 is formed by printing are provided with an adhesive layer 6 or an adhesive resin via a primer layer (not shown). This is a laminated film 15 bonded together. Further, as shown in FIG. 3, a bag body 90 in which a heat seal portion 95 is formed by providing an internal folded portion 91 and an external bent portion 92 in the laminated film 15.

[0011] The bonding layer of the present invention can be selected from thermoplastic resins which are preferably used as a carrier layer capable of stabilizing the film forming process of the entire multilayer film. For example, low-density polyethylene, ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ionomer, nylon 6, copolymer nylon (nylon 6 / nylon 66, nylon 6 / nylon 12), and copolyester Among them, a material that can be formed at 235 ° C. or lower is selected. Preferably, it is a low-density polyethylene having an MFR of 5.0 g or less. When the MFR is 5 g or more, the viscosity of the multilayer film containing EVOH decreases in film formation, and the balloon tends to fluctuate during film formation. Since the HS layer made of LLDPE often comes in contact with the contents as the innermost layer when used as a bag, it is oxidized by air (oxygen) and heat at the time of film formation to generate an odor, and It is preferable to form a balloon for film formation by enclosing an inert gas (carbon dioxide gas and / or nitrogen gas) from the viewpoint of preventing the flavor from being impaired or the product from causing heat seal inhibition. Then, after the film formation is completed, the bonding layer is subjected to a corona discharge treatment immediately after the film formation in order to give a suitable property to the adhesive layer.

The adhesive resin layer is a layer provided for bonding the two layers of resin when the resin for the bonding layer and the barrier layer is coextruded to form a film. The barrier layer is EVO as in the present invention.
When it is composed of H, it can be appropriately selected from graft-polymerized or copolymerized polyethylene containing an acid anhydride, modified ethylene / vinyl acetate copolymer, modified nylon, and the like. Preferably, the same flow characteristics as EVOH and low-density polyethylene are used. Is a graft-polymerized polyethylene containing an acid anhydride having

The higher the proportion of vinyl alcohol, the better the barrier properties of EVOH. However, since the bending strength and the yield point elongation tend to be inferior, those having excellent barrier properties are inferior in pinhole resistance. There is. Therefore, the ethylene content is 25 to 50 mol% (EVOH is 75 to 5 mol%).
(0 mol%) having a relatively large amount of a vinyl alcohol component is also preferable from the viewpoint of maintaining the barrier property. If the ethylene content is less than 25 mol%, the flexibility of the barrier layer is inferior, and it is difficult to avoid a decrease in the barrier property due to the generation of pinholes. The thickness of the barrier layer depends on the required barrier properties. However, in order to achieve the effect of the barrier multilayer HS film (at least the oxygen permeability is 10 cc / 24 h · m ² or less), the thickness of the barrier layer is 50% or more of the total amount of the resin. It is preferable to configure. And it goes without saying that the upper limit is limited to such an extent that the flexibility of the EVOH layer is not reduced.

The cushion layer of the present invention has the function of preventing the generation of pinholes in the barrier layer, and at the same time the bag formed of the barrier multi-layer HS film is sealed and formed by heat sealing. And the effect of preventing the occurrence of pinholes in the laminated film generated at the end of the heat seal portion. Therefore, it is preferable that the constituent polymer has excellent flexibility and that the glass transition point is higher than the use temperature and the softening temperature is lower than the temperature of the HS layer in order to realize the flexibility. Accordingly, polyethylene having a density of 0.915 g / cm ³ or less can be preferably used, but other ethylene / vinyl acetate copolymers, ethylene / acrylic acid copolymers, ethylene / acrylic ester copolymers, ionomers, ethylene / propylene It is also possible to blend rubbers and butyl rubbers which have rubber-like properties regardless of their density.

The total thickness of the barrier multi-layer HS film is preferably about 15 to 100 μm at which ordinary melt extrusion film formation is possible, but is not particularly limited. And the lamination layer,
For the purpose of stabilizing the film formation, the total thickness of the multilayer film is set to 10% or more, the adhesive resin layer is set to a minimum thickness of 2 μm or more that can be formed, and the barrier layer is defined by a desired barrier property. An excellent barrier property can be provided by a composition of 50% by weight or more. The HS layer has a thickness of 5-20.
The thickness of the cushion layer is preferably set as thick as possible to 10 to 40 μm in order to exhibit the effect.

If the film is a co-extrusion multilayer film forming machine, any of a circular die type and a T die type may be used, but a circular die type capable of absorbing a change in the total thickness by rotation of a winding shaft is preferable. The cooling of the produced multilayer film can be performed by air cooling or water cooling. The air-cooled type can set the processing temperature low, so that the generation of gelled substances generated by thermal decomposition from EVOH is small, and the contact / residence time of the resin in the film state in the die is prolonged, so that the adhesive strength between layers is increased. Can be strengthened. The water-cooling method that can suppress the crystallinity of the film is an effective method depending on the resin used, such as using polyamide for the bonding layer.

The formation and adhesion of each layer may be either a feed block method or a multi-manifold method, and may be either in-die bonding or out-of-die bonding. Certain in-die bonding methods are preferred.

As the base film which is laminated with the above-mentioned barrier multi-layer HS film to form a laminated film, one to three kinds of films are used from those which are used as the base material of ordinary film-shaped bags. For example, it can be appropriately selected from stretched or non-stretched films such as polyethylene, polypropylene, polyester, polyamide, and cellulose acetate, paper, cellophane, and the like. Preferably, it is a biaxially stretched polypropylene film which is excellent in bending resistance and advantageous from the viewpoint of cost.

The lamination of the barrier multi-layer HS film and the above film to form a laminated film is performed by wet lamination using an emulsion adhesive, dry lamination using a reaction-curable adhesive, petroleum wax. , Hot-melt adhesives composed of ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-acrylate copolymer, ionomer, synthetic rubber, tackifier, etc. Depending on the material and application, the usual method of hot melt lamination by hot melt lacquer used in the heated state) or sandwich lamination by laminating through a melt-extruded adhesive resin layer with a primer layer as necessary Select and use.

In order to form a bag from a laminated film,
With the above-mentioned substrate film on the outside and the HS layer on the inside, bag making or automatic filling packaging is performed in an appropriate shape. The form of the bag is not particularly limited, such as a pillow bag, a gusset bag having a folded gusset, and the running of the laminated film in a bag making machine can be supplied regardless of whether it is vertical or horizontal.

Hereinafter, the present invention will be described in more detail based on experimental examples. (Examples 1 and 2 and Comparative Examples 1 to 5) The resin compositions of A to F shown below were formed from a melt extruder having a thickness of 50 mm in each of six types and six layers of a feed block type circular die or T die. Using a film machine, a barrier multi-layer HS film of Example and a film of Comparative Example having a processing temperature of 230 ° C. and a total thickness of 50 μm were prepared so as to have the thickness shown in Table 1.

[0022]

[Table 1] The resin composition of each layer and its thickness (unit: μ)
m) and film formation method However, the resin compositions A to F are as follows. A LL with density of 0.915 g / cm ³ and MFR of 4.0 g
LL with DPE B density 0.915 g / cm ³ and MFR 4.0 g
DPE, density 0.915 g / cm ³ , MFR10.
1: 1 mixture with 0 g of LLDPE C LL with density 0.895 g / cm ³ , 1.6 g MFR
DPE D MFR 1.6 g acid anhydride graft polymerized polyethylene E Ethylene content 38 mol%, MFR 1.5 g EVO
LD with HF density of 0.920 g / cm ³ and MFR of 1.6 g
PEI, film formation by circular die method T, film formation by T-die method

The laminating layer 1 of the barrier multi-layer HS film 10 prepared in Examples and Comparative Examples, and a pattern layer 7 are provided by gravure printing on a biaxially oriented polypropylene (base film 8) having a thickness of 20 μm. The surface (adhesive layer 6) coated with the two-component reactive adhesive (adhesive layer 6) is bonded to
The laminated film 15 shown in FIG. 2 was formed. Evaluation of film forming suitability, film forming stability and oxygen permeability, heat sealing start temperature of laminated film, heat seal strength, HS layer slip which is evaluation of bag forming suitability in multilayer films of Examples and Comparative Examples. did. Then, using the laminated film 15, as shown in FIG. 3, the internal folded portion 91, the external folded portion 92, the heat seal portion 95, and the folding width 93 of 50 mm in length × width = 3.
A gusset bag (bag body 90) having a size of 00 × 150 mm ² and a heat seal width of 10 mm was prepared, and the suitability for bag making (and the occurrence of pinholes in the folded portion) was evaluated.

Table 2 shows the evaluation results of the examples and comparative examples.

[Table 2] Evaluation results

The evaluation methods and evaluation criteria for the examples and comparative examples are as follows. (Evaluation method)-Film formation suitability The occurrence frequency of flow unevenness during film formation and the stability of the balloon were comprehensively evaluated visually.・ Oxygen permeability MODE according to JIS K7126 B method (isobaric method)
RN CONTROLLINK. OX-TRAN2
The oxygen permeation amount (cc / atm · m ² 24 h) was measured at 23 ° C. and a relative humidity of 65% by using / 20.・ Heat sealing start temperature Pressure of 1 kg / cm ² , relative to HS layer of laminated film
After heat sealing to 10 mm width under the condition of × 1 sec,
It is cut at a width of 15 mm perpendicular to the heat sealing direction, and its peel strength is measured at a peel speed of 300 mm / min.
The temperature at which the strength became 2 kg / 15 mm was defined as the heat sealing start temperature. Heat Seal Strength The peel strength (g / 15 mm width) of the heat seal portion measured at 150 ° C. under the above conditions was defined as the heat seal strength. -Appearance of film The film formation was continued for 10 hours with the above resin composition, the frequency of gel generation, and the transparency of the film (JIS K7105-1)
981).・ Coefficient of dynamic friction The slip of the HS layer of the laminated film against the stainless steel surface is J
It was measured according to IS K7214-1987. -Suitability for bag making (sealability) After a laminated film is made with a vertical pillow type bag making machine, a pinhole check solution (alcohol-soluble dye dissolved in octyl alcohol and colored) Liquid) was injected, and the presence or absence of permeation into the seal portion was confirmed. Evaluation criteria ◎ Very good. ○ Good, no problem in practicality. △ Although there are some problems, it can be put to practical use by selecting the application. X Many disadvantages and no practicality.

Examples 1 and 2 are excellent multilayer HS films having a good balance of film forming aptitude, stable barrier properties, heat sealing properties, and bag making aptitude. In particular, the structure of Example 2 has a good balance of MFR between the layers and is excellent in film-forming suitability. On the other hand, the film of Comparative Example 1 is inferior in film formation suitability because it is located on the surface at the time of EV film formation, and a decrease in barrier properties due to moisture absorption is also observed. Comparative Example 2
And 3 are poor in bag making suitability, and Comparative Examples 3 and 4 are films having poor film forming suitability.

[0027]

As described in detail above, the barrier multi-layer HS film of the present invention comprises an LLDPE capable of stably forming a multi-layer co-extruded film and an HS layer (an inner layer of a balloon at the time of forming a circular die). ) And LDPE
, The suitability for film formation is extremely stable. E with excellent barrier properties
VOH occupies 50% or more of the whole multilayer film and barrier property multilayer H in which barrier property is prevented from lowering due to moisture sandwiched between LLDPE and LDPE excellent in moisture proof property.
It is an S film. Also, sandwiched EVOH
In the method for forming a circular die, there is little opportunity to decompose by contact with air, and the film has stable film forming aptitude. Therefore, there is an effect that a co-extruded film having a good balance between barrier properties, sealing properties, and bag making properties can be provided.

[Brief description of the drawings]

FIG. 1 is a view showing a concept of a cross section of a barrier multi-layer HS film.

FIG. 2 is a conceptual diagram of a cross section of a laminated film using a barrier multilayer HS film.

FIG. 3 is a perspective view showing the concept of a pillow bag formed from a laminated film of a barrier multilayer HS film.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lamination layer 3 Barrier layer 4 Cushion layer 5 HS layer 6 Adhesive layer 7 Picture layer 8 Base film 10 Barrier multilayer HS film 15 Laminated film 21, 22 Adhesive resin layer 90 Bag body 91 Internal folding part 92 External folding Bent part 95 Heat seal part

Claims (3)

[Claims] 1. A material having a density of at least 0.900 to 0.92.
Heat sealant layer made of linear polyethylene of 0 g / cm ^3, a cushion layer density of the plastomer layer of 0.880~0.895g / cm ^3, the adhesive resin layer, an ethylene content of 25 to 50 mol%, saponification It is characterized by being formed by laminating an ethylene / vinyl alcohol copolymer having a conversion rate of 90% or more, a gas barrier layer comprising 50% by weight or more, an adhesive resin layer, and a bonding layer comprising a thermoplastic resin. Gas barrier multilayer heat seal film. 2. The gas barrier multi-layer heat seal film according to claim 1, wherein the resin constituting the heat sealant layer and the resin constituting the bonding layer has a melt flow ratio of less than 5 g. 3. A material having a density of at least 0.900 to 0.920.
heat sealant layer made of linear polyethylene of g / cm ^3, a cushion layer density of the plastomer layer of 0.880~0.895g / cm ^3, the adhesive resin layer, an ethylene content of 25 to 50 mol%, saponification Film formation of a gas barrier layer comprising 50% by weight or more of an ethylene / vinyl alcohol copolymer having a conversion ratio of 90% or more, an adhesive resin layer, and a bonding layer comprising a thermoplastic resin by a circular die method, and A method for producing a gas barrier multi-layer heat seal film, which is performed at a temperature of 235 ° C. or lower.