JP2869136B2 - Easy peel polypropylene film and sheet - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a polypropylene-based multilayer film and sheet, and more particularly, to a heat seal usable for a boil, a retort-sterilizable bag, a lid, a molded container, and the like. The present invention relates to a composite easy-peelable polypropylene film and sheet having both easy-peelability and easy-peelability.

(Prior Art) Conventionally, several easy-peeling configurations that have both heat sealability and easy-peelability that can be sterilized by boiling and retorting have been proposed.

For example, (A) polypropylene or polypropylene-based
JP-B-56-18467 discloses a method using polyethylene or a polyethylene or a mixture with other polyolefins.
No., JP-B-61-60100, JP-A-57-131556, JP-A-6-131556
No. 2-109768, JP-A-63-179741 and the like.

On the other hand, (B) the polypropylene layer is the innermost layer,
Several delamination-type composite films with an adjacent layer have also been proposed.

For example, it is described in Japanese Patent Publication No. 54-5356 or Japanese Patent Application Laid-Open No. 62-117741.

In addition, the present inventors have also proposed (C) an easily openable container capable of retort sterilization, in which an easily cohesive fracture polypropylene film is compounded in the innermost layer of the container.
JP-A-59-31574, a heat-resistant sealed container prepared by modifying a method of imparting easy cohesive failure to polypropylene,
Japanese Patent Application Laid-Open No. 59-199458 has been proposed.

(Problem to be Solved by the Invention) However, the method according to the above (A) is
At least 30% by weight of polyethylene or polyethylene-based or other polyolefin for easy release
The above mixing is necessary, and the heat resistance of the inherent polypropylene is greatly reduced, so that there is anxiety in the heat sterilization treatment such as boiling and retorting.

Furthermore, depending on the content of the food to be packaged, this type of mixture is particularly useful for the transfer of odors such as polyethylene or polyethylene or other polyolefins to foods and the transfer of taste from foods to packaging materials. After the heat sterilization treatment such as boiling and retorting, there is a defect that the taste of the content food is changed.

Next, in the method according to the above (B), the layer adjacent to the innermost polypropylene layer is also made of polyethylene or polyethylene based on 30% by weight or more, or another polyolefin in order to impart easy peelability. It is particularly necessary to mix heat-resistant foods such as stew with curry solution, fish and meat, etc. during heat sterilization of boil, retort, etc. due to a decrease in heat resistance. By the penetration of oils and fats from the food,
It is greatly affected and the seal part may rupture.

Further, when the filled package is reheated in a microwave oven, the result is that the temperature of the oil-fat portion cannot be increased at 150 ° C. or more at all.

In the method according to (C) described above,
(A) and (B) are methods in which easy peeling is obtained without reducing the heat resistance as much as possible. Therefore, very good results have been obtained in terms of heat resistance. Unfortunately, there was a problem in that it could be opened by girls, the elderly, children, etc. without resistance.

The present invention has been made in order to solve such problems, and when used as a heat seal sealant for packaging materials, boil, retort, etc. can be subjected to heat sterilization in an oil-fat food packaging, and further, Provide easily peelable polypropylene films and sheets that can be used in easily peelable packages that can be sufficiently opened to girls, elderly people, children, etc., without enduring microwave oven heat treatment and without affecting the taste change of taste. The purpose is to do.

(Means for Solving the Problems) The present invention is a polypropylene-based co-extruded film and sheet, wherein both the inner layer and the intermediate layer on the heat-sealed surface have easy cohesive failure, and the outer layer has easy cohesive failure. It does not have characteristics.

The inner layer of polypropylene has a tensile strength of 150 kg / cm ² or more,
It has an elongation of 100% or less, preferably a tensile strength of 200 to 300 kg / cm ² and an elongation of 300 to 60%, and is obtained from a mixed resin of crystalline homopolypropylene and crystalline propylene-ethylene copolymerized polypropylene.

As long as the properties of the mixed resin are not substantially impaired, amorphous propylene-α is used for the purpose of improving impact strength and the like.
An olefin copolymer resin may be further mixed in a small amount.

The mixed resin will be described with an example.
Weight% of a mixture of a crystalline propylene-ethylene block copolymer (d = 0.91, MFR = 0.5) and a crystalline homopolypropylene (d = 0.90, MFR = 30); A range of 80% by weight is suitable.

However, the desired properties are different in the polymerization method, and
This is obtained by mixing both resins having remarkably different thermal fluidities, and therefore, the mixing ratio is adjusted by the difference in thermal fluidity between the two resins.

The interlaminar strength of the film formed from these mixed resins is appropriately in the range of 1.8 to 2.8 kg / 15 mm, but is preferably in the range of 2.0 to 2.5 kg / 15 mm.

Next, as for the intermediate layer, the mixed resin used for the inner layer contains 20% by weight or less, preferably 8 to 15% by weight of polyethylene, and the polyethylene is preferably high-density polyethylene.

The tensile strength of the mixed resin of this intermediate layer is 150 to 250 kg / cm ² ,
Those with an elongation of 100% or less are appropriate.

The film interlayer strength of the film molded from the mixed resin in this range indicates 0.3 to 1.0 kg / 15 mm,
Preferably, it can be said that the range is 0.5 to 0.8 kg / 15 mm.

The polypropylene used for the outer layer has a tensile strength of 300 kg / cm ² ,
A general-purpose film having an elongation of 200% or more and having no cohesive failure property, a cast film having an interlayer strength of 3.0 kg / 15 mm or more, and sheet grade polypropylene are used.

The next important element of the present invention is the thickness configuration of the inner layer and the intermediate layer, each having an appropriate thickness of 3 to 15 μm, preferably 5 to 10 μm.

When the thickness is 3 μm or less, the sealing strength is apt to be weak.
When the thickness is 15 μm or more, the sealing strength tends to be strong, and the sealing strength tends to be unstable.

Mixing of the resin in the present invention is performed by dry blending with a mixer, a blender, or the like, which is a common means in the art, and then pelletizing by hot kneading with an extruder.

Other additives may be added in a range that does not affect the performance of the present invention.

For example, a plastic resin, a lubricant, a filler, a surfactant, an antioxidant, an ultraviolet absorber, an oxygen absorber, a conductive agent and the like can be mentioned.

Further, a barrier resin, for example, an ethylene-vinyl alcohol copolymer or a polyvinylidene chloride-based resin may be coextruded into the intermediate layer of the outer polypropylene layer.

In the resin properties described in the present invention, d
Is the density according to JIS-K-7112, MFR (Melt Flow Ra
te) is based on JIS-K-7210, and the test method of tensile strength and elongation is based on JIS-K-6758.

Further, the measurement of the interlayer strength of the film was performed by performing a T-die casting on a single-layer film having a thickness of 50 μm for each layer at an extrusion temperature of 230 ° C., performing a corona treatment on the bonding surface of the film, and then stretching the film to a thickness of 15 μm. Then, the sealant surfaces of the samples subjected to dry lamination with a urethane-based adhesive were heat-sealed to a width of 10 mm under the conditions of a seal pressure of 2.0 kg / cm ² and a seal time of 1.0 second at a heat seal temperature of 180 ° C. The sample in the width direction of the seal.
A peeling test was performed using a Tensilon tensile tester under the conditions of a peeling speed of 300 mm / min and a peeling angle of 90 ° according to the mm width.

The easily peelable polypropylene film and sheet of the present invention are manufactured by a co-extrusion casting method, and a feed block type T-die casting is preferable, but may be manufactured by an inflation method.

The method of combining the film with other substrates thereafter includes dry lamination, polyolefin sand lamination,
A wide range of methods such as thermal lamination can be applied.

The sheet is used for forming lids, containers and the like by thermoforming such as vacuum forming.

(Operation) The operation of the present invention will be described with reference to the drawings.

FIG. 1 shows the structure of the easily peelable polypropylene film and sheet of the present invention. Each structure of the film and sheet has the following features.

That is, <Inner layer 1> Cohesive failure high heat resistance thin film polypropylene layer <Intermediate layer 2> Cohesion failure medium heat resistance Thin film polypropylene mixture layer <Outer layer 3> Non-cohesive failure high heat resistance Thick film polypropylene layer They are bonded in a fused state by extrusion.

The easily peelable polypropylene film of the present invention is combined with a base film 4 having high heat resistance and high tensile strength, such as a biaxially stretched polyester film or a stretched nylon film, and the sealant faces of the present invention of the composite are heat-sealed. FIG. 2 shows a state in which heat sealing is performed by the bar 5.

FIG. 3 shows a state where the sealant surface and the polypropylene film or sheet surface are heat-sealed.

FIGS. 4-1 and 4-2 show the respective peeled states.

As described above, first, the inner layer 1 and the intermediate layer 2 of the sealant layer corresponding to the heat seal bar end 5 'in FIGS. 4-1 and 4-2 are cohesively broken in the thickness direction by the peeling force. From the middle layer 2 in the width direction of the heat seal, the cohesive failure occurs again in the thickness direction at the final heat seal bar end 5 ″, and the peeling is completed.

 The coherently broken portion is transferred 9 to the adherend surface.

This peeling action can be achieved only by the structure and features of the present invention. Incidentally, the conventional type in which the inner layer polypropylene layer has no easily cohesive failure property, and delaminates at the interface between the inner layer and the intermediate layer. The peeling mechanism is such that the inner layer / intermediate layer at the end of the heat seal is first peeled off by peeling force, and then the inner polypropylene layer is torn off. Also, the cut surface of the inner layer in the thickness direction becomes unstable, which greatly impairs the commercial value.

In the inner layer polypropylene which is one element of the present invention,
As described above, the method of imparting easy cohesive failure is, for example,
As one method, when formed into a film by mixing polypropylenes having remarkable differences in physical properties such as elongation or thermal fluidity, by dispersing those resins appropriately, it is considered that they show physical properties such as brittleness. However, the present invention is not limited by the theory.

(Embodiment) An embodiment of the present invention will be described in detail below using an example.

Example 1 (A) Crystalline propylene-ethylene block copolymer (d = 0.91, melting point 1) containing 6% by weight of ethylene component having MFR = 0.5
MFR = 60 ° C, tensile strength 350kg / cm ² , elongation 500%)
30 (B) crystalline homopolypropylene (d = 0.90, melting point 1
68 ° C, tensile strength 180 kg / cm ² , elongation 140%)
After dry blending at (A) / (B) = 1/1, the mixture was pelletized with an extruder heat kneading device at an extrusion temperature of 200 ° C. to obtain a mixed resin for the inner layer.

By the way, this mixed resin has a tensile strength of 280 kg / cm ² and an elongation of
The film interlayer strength was 50% and the interlaminar strength was 2.3kg / 15mm.

Next, d = 0.95, MI (ASTM D-1)
505) = 4.5 A resin obtained by mixing 15% by weight of high-density polyethylene was used as a resin for the intermediate layer.

Incidentally, the properties of the mixed resin are as follows: tensile strength 200 kg / cm ² , elongation
80%, the interlayer strength of the film was 700 g / 15 mm.

The resin for the outer layer is a general-purpose film-grade crystalline homopolypropylene having an MFR of 9.0 (d = 0.90,
For the sheet, a general-purpose sheet-grade crystalline homopolypropylene with MFR = 2.3 (d = 0.90, melting point 168 ° C, tensile strength 37) was used, using a melting point of 168 ° C, tensile strength of 340 kg / cm ² , and elongation of 700%.
(0 kg / cm ² , elongation: 700%), a T-die co-extrusion film caster was used to obtain a 50 μm thick film having an extrusion temperature of 230 ° C. and an outer layer of 40 μm / intermediate layer of 5 μm / inner layer of 5 μm.

 The outer layer surface was subjected to an in-line corona treatment.

Then, using a T-die co-extrusion sheeting apparatus, a 765 μm thick sheet having an extrusion temperature of 240 ° C. and an outer layer of 705 μm thick / intermediate layer of 10 μm / inner layer of 5 μm was obtained.

The performance of the easily peelable polypropylene film and sheet obtained in this manner will be described in Examples according to applications.

<Bag> A sample in which the biaxially stretched nylon 6 film 15 μm thick (d = 1.15, melting point = 220 ° C.) and the prepared 50 μm thick film were dry-laminated with a two-component urethane adhesive and the adhesive was sufficiently cured. Under the conditions of a heat seal temperature of 180 ° C., a pressure of 2 kg / cm ² and a time of 1 second, a three-sided bag having a size of 25 cm (length) × 18 cm (width) was prepared with a seal width of 10 mm.

After the bag was filled with cooked beef stew and degassed, the mouth was hermetically sealed under the above conditions.

 The opening force before the retort sterilization treatment was 1.5 kg / 15 mm.

This bag was subjected to a retort sterilization treatment at 125 ° C. for 30 minutes.

No abnormalities such as bag breakage and appearance during retort treatment were observed.
When you peel off the two laminated films by hand from the opening start,
The heat-sealed fused portion was cohesively broken and could be easily opened.

 The opening force after this treatment was stable at 1.4 kg / 15 mm.

The taste of the beef stew was as delicious as before filling.

<Lid material> A beef stew was filled into a molded container having an outer dimension of 120 φ (flange width 10 mm) and a depth of 25 mm vacuum-formed from an 800-μm-thick polypropylene sheet and laminated on the above-mentioned biaxially stretched nylon film. The composite film is then used as a lid, and the container is heat-sealed at a temperature of 180 ° C and a pressure of 10k.
Heat sealing was performed using a cup sealer under the conditions of g / cm ² and a time of 1 second.

 The opening force before the retort sterilization treatment was 1.7 kg / 15 mm.

This container was retorted at 125 ° C for 30 minutes.No abnormality was observed during the retort treatment. Was.

The peeled surface was also clean without stringing, swelling and the like.

<Container> The 765 μm-thick sheet obtained above was vacuum-formed to form a thermoformed container having an outer dimension of 120φ (flange width 10 mm) and a depth of 25 mm.

This container is filled with beef stew, and a previously laminated biaxially stretched nylon film 15 μm × retort food general-purpose polypropylene film 60 μm is used as a lid material having a dry laminate structure.
A hermetic seal was performed under the same conditions as in the above.

The opening force of this product before retort sterilization is 2.5kg / 15mm
Met.

This container was subjected to a retort treatment at 125 ° C. for 30 minutes, but no abnormality occurred.

The opening force after the treatment was very stable at 2.45 kg / 15 mm.

And, due to the remarkable effect that the amount of plastic deformation of the peeled portion obtained when the easily peelable sealant having the cohesive failure property is formed on the container side is small, it is easy for girls, elderly people, and children for the opening force strength. But I was able to open it.

 The peeled surface was clean without stringing or scum.

Microwave heating was performed in a state in which steam permeability was imparted by peeling off part of the retort-treated product, but despite the fact that the temperature of the oily surface of the contents rose to 150 ° C, No abnormality occurred in the container.

The heated beef stew was tasted and was as delicious as before filling.

Example 2 (C) Crystalline random copolymer polypropylene having 3% by weight of ethylene component having MFR = 9.0 (d = 0.90, melting point = 165)
C), tensile strength of 320 kg / cm ² , elongation of 600%), MFR = 50 D) crystalline homopolypropylene (d = 0.90, melting point = 168)
° C, tensile strength 190 kg / cm ² , elongation 50%) by weight ratio (C)
/ (B) = 2/3, and 10% by weight of a non-crystalline polypropylene-α copolymer (Tuffmer XR, X-107L manufactured by Mitsui Petrochemical Industry Co., Ltd.) as a modifying resin for the purpose of imparting impact resistance.
After the dry blending, it was compounded into a pellet at an extrusion temperature of 200 ° C.

 This mixed resin was used as an inner layer resin.

By the way, this mixed resin characteristic has a tensile strength of 200 kg / cm ² , elongation
70%, film interlayer strength 1.8 kg / 15 mm.

Next, as in Example 1, a resin in which 5% by weight of high-density polyethylene was mixed with the mixed resin was used as a mixed resin for an intermediate layer.

Incidentally, the properties of the mixed resin are as follows: tensile strength 160 kg / cm ² , elongation
The film had an interlaminar strength of 50 g / 15 mm.

As the resin for the outer layer, the same polypropylene resin as in Example 1 was used for both the film and the sheet.

The results of a test conducted using these resins in exactly the same manner as in Example 1 except for the retort treatment temperature will be described.

<Bag> Beef stew was filled, and a retort sterilization treatment was performed at 120 ° C. for 30 minutes.

The opening force before retort was 1.2 kg / 15 mm. The opening force after retort was 1.1 kg / 15 mm.

There was no abnormality after retorting, the opening was performed smoothly, and the peeled surface was clean.

The taste of the beef stew was as delicious as before filling.

<Lid material> Fill beef stew into a polypropylene container and place it at 120 ° C.
A retort sterilization treatment of × 30 minutes was performed.

The opening force before retort was 1.5 kg / 15 mm. The opening force after retort was 1.4 kg / 15 mm.

There was no abnormality after retort, opening was easy, and the peeled surface was clean.

<Container> Beef stew was filled in the same manner as described above into a molded container made of the constituent sheet of the present invention, and subjected to a retort sterilization treatment at 120 ° C for 30 minutes.

The opening force before retort was 2.0 kg / 15 mm. The opening force after retort was 1.9 kg / 15 mm.

There was no abnormality after the retort, and the opening was easy for girls, the elderly, and children, and the peeled surface was clean.

The taste of the beef stew was as delicious as before filling.

(Comparative Example) 1) The same method as in Examples 1 and 2 was used, except that the crystalline homopolypropylene or the crystalline random copolymer polypropylene of the inner layer resin used in Example 1 or 2 was used alone as the inner layer resin. However, since the layer does not have cohesive and destructive properties, the opening strength is increased in all cases of bags, lids, and containers. Was difficult.

In addition, the peeled surface that was opened was inconvenient because the cutting of the inner layer portion was unstable, resulting in loss of commercial value.

2) When the content of polypropylene in the intermediate layer resin used in Example 1 or 2 is 5% by weight or less, the interlayer strength of the film of the intermediate layer is increased and the opening strength is increased. Etc., it was easy to open.

In the case where polyethylene is mixed in an amount of 20% by weight or more, the seal strength after retort of oil-based food is greatly reduced due to the decrease in heat resistance, and the instability of the seal protection strength is caused due to instability. .

3) In the thickness configuration of the present invention, the layer thicknesses of the inner layer and the intermediate layer, which are easily cohesively destroyed, are each 3 to 15 μm thick,
When the thickness is 3 μm or less, the peeling force is weak and unstable,
When the thickness is 15 μm or more, the peeling force is strong and unstable, so that practical anxiety arises.

4) By mixing 5 to 10% by weight of high-density polyethylene with the inner layer resin, more easily cohesive and peeling properties were obtained, but in the case of highly flavored oily foods such as curry liquid and beef stew, the taste was greatly reduced. Practical problems arose.

(Effect of the Invention) The following effects can be obtained by the packaging material using the easily peelable polypropylene film and sheet of the present invention as a sealant.

a.In the fused part formed between the sealant layers, in order to be opened by cohesive failure at the time of opening,
Since there is no need to cut a part having a large physical strength, the part can be easily opened by the hand of a girl, an old man or a child.

Naturally, there is no problem of so-called delamination in which the sealant layer and the base material are separated.

b. Since the innermost layer of the sealant is polypropylene and does not contain other polyolefins such as polyethylene, it is advantageous in changing the taste of the content food.

Furthermore, since it has high heat resistance, high-temperature sterilization treatment of boiling, retorting, and the like can be performed.

c. It can be used in a wide range of fields due to the features of the configuration of the present invention, such as bags, lids, and containers.

d. The packaging material using the sealant of the present invention can be used as curry liquid, borscht, beef stew, meat sauce, pork tea, hamburger, Chinese food, boiled rice, cooked rice, red beans, soybeans, and other boiled foods and retort foods.

e. Since the opening is performed by easily cohesive failure, a clean peeling surface is generated without the fluffing or swelling of the peeling surface.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial sectional view showing an easily peelable polypropylene film and sheet according to the present invention. 2 and 3 are cross-sectional views showing a state of heat sealing. FIG. 4-1 is a sectional view showing the peeled state in FIG. 2, and FIG. 4-2 is a sectional view showing the peeled state in FIG. 3, respectively. In the figure, 1 is an inner layer, 2 is an intermediate layer, and 3 is an outer layer.

Claims (2)

(57) [Claims] 1. A co-extruded film or sheet comprising the following outer layer, intermediate layer, and inner layer mainly composed of polypropylene having different film interlayer strengths, and said film and sheet are used as a heat seal sealant of a packaging material. By this, when the polypropylene and the film and the sheet or the film, and the sheet is peeled off after heat sealing, the inner layer and the intermediate layer of the film and the sheet are easily peeled by cohesive failure. An easily peelable polypropylene film and sheet characterized by the above-mentioned. I. Outer layer A crystalline homopolypropylene or a crystalline propylene-ethylene copolymerized polypropylene film and sheet layer having an interlaminar strength of 3.0 kg / 15 mm or more and having no cohesive failure property. B. Intermediate layer Mixed resin of crystalline homopolypropylene and crystalline propylene-ethylene copolymerized polypropylene, polyethylene
A mixed resin film layer having an interlaminar strength of 0.3 to 1.0 kg / 15 mm and having an easily cohesive fracture property by a mixed resin in which 20% by weight or less is mixed. C. Inner layer A mixed resin film layer having an interlaminar strength of 1.8 to 2.8 kg / 15 mm and having an easily cohesive fracture property, made of a mixed resin of crystalline homopolypropylene and crystalline propylene-ethylene copolymerized polypropylene. 2. The co-extruded film and the inner layer having an easily cohesive fracture property of the sheet and the intermediate layer each have a thickness of 3 to 15 μm.
The easily peelable polypropylene film and sheet according to the above.