JPH0976431A - Sealant film for retort - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent impact resistance and low-temperature salability of a sealant film by laminating a sealant layer made of specific weight ratio of random polymer polypropylene resin and ethylene elastomer on one surface of a core layer made of specific weight ratio of polypropylene resin and ethylene elastomer. SOLUTION: The sealant film for retort comprises a sealant layer of the layer brought into direct contact with food to be packaged and adhered to other packaging material disposed at the opposite side of the food, and a core layer laminated on the sealant layer to reinforce it. The sealant layer contains 70 to 90 pts.wt. of random copolymer polypropylene and 10 to 30 pts.wt. of ethylene elastomer. The core layer contains 10 to 70 pts.wt. of polypropylene and 90 to 30 pts.wt. of ethylene elastomer. If the mixing ratio of the polypropylene resin exceeds 70 pts.wt. and the mixing ratio of the ethylene elastomer is less than 30wt.%, the heat sealable strength and impact resistance of the obtained sealant film cannot be sufficiently developed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a sealant film for retort.

[0002]

2. Description of the Related Art In recent years, the demand for retort pouch foods has increased more and more with the increase in the number of elderly people and single-person households, as well as the increase in the number of individuals eating and working together. Processed food contained in a container (hereinafter referred to as a retort pouch) has been widely used because of its ease of processing, distribution, and use. Furthermore, large cooked foods containing 1 kg or more for business use have been changed from canned to retort pouches.

In the soft packaging material used for the retort pouch, scratches such as pinholes and other notches are severely checked from the viewpoint of hygiene of processed foods contained therein and safety of packaging. As described above, due to the increase in the number of packaging units, hygiene and safety for flexible packaging materials are increasingly demanded.

For the above-mentioned flexible packaging material, for example, JP-A-4
JP-A-9-20247 discloses a resin component consisting of high-density polyethylene having a molecular weight of 50,000 to 120,000 and a melt index of 10 or less and crystalline polypropylene having a melt index of 1 to 8, an ethylene content of 85 mol% or less, and a Mooney viscosity of 30 to. 20 ethylene-propylene copolymer rubber of 130
Disclosed is a polyolefin film for packaging, which is based on a resin composition containing about 35% by weight.

[0005] Japanese Patent Application Laid-Open No. 5-262900 discloses that
Ethylene component 1.5 to 3.5% by weight, melt flow rate 5 g / 10 min or more, ortho-dichlorobenzene is used as a solvent, and the amount of the extracted component by the cross fractionation method at a temperature of 80 ° C. is 20% by weight or less. Is propylene-
Disclosed is a polypropylene unstretched film composed of a composition of an ethylene copolymer and an ethylene copolymer having a density of 0.91 g / cm ³ or less.

The polyolefin film for packaging disclosed in JP-A-49-20247 is also disclosed in JP-A-5-262.
The polypropylene unstretched film disclosed in Japanese Laid-Open Patent Publication No. 900 also does not provide sufficient improvement in impact strength and the like required for the flexible packaging material used for the retort pouch, and the raw resin selection range is narrow. There is a case in which the film is not sufficiently kneaded and dispersed in a film extrusion molding machine which is generally used just by mixing, and in advance, kneading by heating with a twin-screw extruder or the like and pelleting the raw material resin, etc. This is a raw resin or film that is extremely difficult to use or cumbersome because it requires a mixing operation and a post-treatment such as annealing the formed film to control the elastic modulus of the film.

Further, in JP-A-59-115312, 60 to 95% by weight of the total polymer composition is added to the propylene content of 90% by weight in the first step in the presence of a transition metal catalyst component and an organoaluminum catalyst component. % Or more and melting point 135
It is copolymerized with propylene and ethylene and / or an α-olefin having 4 to 12 carbon atoms so that the temperature is ˜155 ° C., and 5 to 40% by weight of the total polymer composition is polymerized after the second step, but the average Polymerized so that the composition has a propylene unit of 10 to 50 mol%, an ethylene unit of 50 to 90 mol%, other α-olefin units of 3 mol% or less, and an average solution viscosity after the second step is 2.5 or more. A polymer for a retort film, in which the production amount, composition and molecular weight of each component are adjusted so that the ethylene content of the total polymer composition is 5.5 to 17% by weight and the melt flow index is 0.5 to 15 g / 10 minutes. A method of making the composition is disclosed.

However, the polymer composition for a retort film disclosed in the above-mentioned JP-A-59-115312 is a retort film generally referred to as a high retort film, which is sterilized at a high temperature of about 135 ° C. A polymer composition for use, which provides an opaque film having a high heat-sealing temperature, is difficult to use under severe operating conditions such as a low food filling processing speed.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above facts, and an object thereof is to provide a retort sealant film excellent in impact resistance and low temperature sealability. It is in.

[0010]

The present invention according to claim 1 provides a core layer comprising 10 to 70 parts by weight of a polypropylene resin and 90 to 30 parts by weight of an ethylene elastomer.
A sealant film for a retort is characterized in that a sealant layer composed of 70 to 90 parts by weight of a random copolymerized polypropylene resin and 30 to 10 parts by weight of an ethylene elastomer is laminated.

According to a second aspect of the present invention, the elution amount in each temperature range by the cross fractionation method is 45 to 80% by weight at 10 ° C. or less based on the total weight, and 5 to 45 at 10 ° C. or more and 75 ° C. or less.
% By weight, 0 to 20% by weight above 75 ° C and below 95 ° C, 95 ° C
70 to 90 parts by weight of a random copolymerized polypropylene resin, ethylene on one surface of a core layer made of a polypropylene resin having a weight average molecular weight in the range of 80,000 to 500,000, which is 5 to 35% by weight at a temperature of less than 125 ° C. System elastomer 30-
The gist of the present invention is a retort sealant film comprising a sealant layer composed of 10 parts by weight.

In the present invention, the sealant layer refers to a layer which is in direct contact with the food to be packaged and which is adhered to the sealant layer or other packaging material located on the opposite side of the food to be packaged,
A film that can be heat-bonded at a temperature as low as possible, which is higher than the retort treatment temperature, is preferable. In the retort sealant film of the present invention, the random copolymer polypropylene-based resin 7
A sealant layer composed of 0 to 90 parts by weight and 10 to 30 parts by weight of an ethylene elastomer is used. The random copolymer polypropylene-based resin is a polypropylene obtained by copolymerizing ethylene as a comonomer, preferably 1 to 4% by weight.

When the copolymerization ratio of the above-mentioned comonomer is less than 1% by weight, the heat-sealing temperature becomes high and the processing speed for filling and processing foods becomes low. On the other hand, if the copolymerization ratio of the comonomer exceeds 4% by weight, the melting point of the sealant layer will be low and blocking will easily occur during the retort treatment. The melt flow rate (MFR) of the random copolymer polypropylene resin is not particularly limited, but is 2 to 15 g / 10 minutes, preferably 5 to 10 g / 10 minutes at 230 ° C.

The above ethylene-based elastomer is a random copolymer of two or more olefins structurally, and from this point, it is similar to the above-mentioned random copolymerized polypropylene resin, but the above ethylene-based elastomer is The difference is that the comonomer has a high olefin content. The comonomer content of the ethylene-based elastomer used in the present invention depends on the type of comonomer,
Although the preferred range varies, it is generally 5 to 40% by weight, more preferably 10 to 35% by weight.

When the comonomer content is less than 5% by weight, the impact resistance of the obtained retort sealant film is lowered, and the comonomer content is 40% by weight.
When it exceeds the above range, the blocking property of the obtained retort sealant film is increased, and blocking is likely to occur during the retort treatment. Examples of the ethylene-based elastomer include ethylene-propylene rubber and ethylene-butene-1 rubber, manufactured by Mitsui Petrochemical Co., Ltd., trade name: Toughmer (A series, P series), manufactured by Japan Synthetic Rubber Co., Ltd., trade name. : EP, EBM, products manufactured by Sumitomo Chemical Co., Ltd., trade names: Excellen, Esplen, etc. can be obtained.

The molecular weight of the ethylene elastomer is
The melt viscosity in the molten state during film formation is selected to be substantially the same as or lower than that of the random copolymer polypropylene resin. When the molecular weight of the ethylene-based elastomer is excessively large, during film forming, the compatibility with the random copolymer polypropylene-based resin is deteriorated, gelation is not sufficiently performed, and the heat seal strength and resistance of the obtained retort sealant film are reduced. The impact strength cannot be sufficiently expressed.

The mixing ratio of the random copolymer polypropylene resin to the ethylene elastomer is preferably about 90 to 70% by weight of the random copolymer polypropylene resin and about 10 to 30% by weight of the ethylene elastomer. When the random copolymer polypropylene resin exceeds 90% by weight, the impact resistance of the obtained retort sealant film becomes low, and when it is less than 70% by weight, the blocking property of the obtained retort sealant film increases, Blocking is likely to occur during the retort treatment.

The kneading of the random copolymer polypropylene resin and the ethylene elastomer is not particularly limited, and examples thereof include a method using a Banbury mixer, a calender roll, a single screw or a twin screw extruder.

In the present invention, the core layer is a layer which is laminated on the sealant layer and reinforces the sealant layer.
In the described invention, polypropylene resins 10-7
A resin composition comprising 0 parts by weight and 90 to 30 parts by weight of an ethylene elastomer is used. The polypropylene resin is not particularly limited, but examples thereof include homopolypropylene, random copolymer polypropylene, block copolymer polypropylene and the like. The polypropylene resin preferably has an MFR in the range of 10 g / 10 minutes or less at 230 ° C.

As the ethylene-based elastomer, the one based on the same technique as the ethylene-based elastomer used for the sealant layer can be used. The type and content of the comonomer copolymerized with ethylene can be selected from the same range as above. The mixing ratio of the polypropylene resin and the ethylene elastomer is 10 to 70% by weight of the polypropylene resin, preferably 40 to 70% by weight, and 90 to 30% by weight of the ethylene elastomer, preferably 60 to 30% by weight. The mixing ratio of the polypropylene resin is 70% by weight
When the mixing ratio of the ethylene-based elastomer is less than 30% by weight, the heat seal strength and impact strength of the obtained retort sealant film cannot be sufficiently exhibited. Also, the mixing ratio of the polypropylene resin is 1
Less than 0% by weight, the mixing ratio of ethylene elastomer is 9
When it exceeds 0% by weight, the obtained retort sealant film becomes a so-called non-flexible film, and blocking becomes large, so that retort treatment becomes difficult.

Further, in the present invention according to claim 2, the elution amount in each temperature range by the cross fractionation method is 45 to 80% by weight at 10 ° C. or less with respect to the total weight, and more than 10 ° C. and 75 ° C. or less. 5 to 45% by weight, 0 to 20% by weight above 75 ° C and 95 ° C, 5 to 35% by weight above 95 ° C and 125 ° C,
A polypropylene resin having a weight average molecular weight of 80,000 to 500,000 is used.

The polypropylene resin is mainly composed of a propylene component, and ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1
-A copolymer obtained by copolymerizing an α-olefin component such as heptene and 1-octene. The polypropylene-based resin is produced, for example, by a multistage polymerization method as shown below. First, as a first step, polymerization is carried out in the presence of a titanium compound catalyst and an aluminum compound catalyst, using a propylene monomer and, if necessary, an ethylene monomer and an α-olefin monomer. At this stage, a propylene homopolymer, a propylene-ethylene copolymer, a propylene-α-olefin copolymer and the like are obtained.

Then, in the second step, the titanium compound catalyst and aluminum compound catalyst, propylene homopolymer, propylene-ethylene copolymer, propylene-α.
A polypropylene resin is obtained by adding a propylene monomer, an ethylene monomer and an α-olefin monomer to a reaction liquid containing an olefin copolymer and copolymerizing the reaction liquid. Similarly, as a third step or more multi-step, in the reaction liquid containing the titanium compound catalyst and the aluminum compound catalyst, propylene homopolymer, propylene-ethylene copolymer, propylene-α-olefin copolymer, etc., propylene Monomer, ethylene monomer,
It is also possible to copolymerize by adding an α-olefin monomer.

The polypropylene resin obtained by the above-mentioned multi-step polymerization reaction may be a propylene homopolymer, a propylene-ethylene copolymer or a propylene-α-olefin copolymer depending on the selection of the monomer. The weight average molecular weight of the polypropylene resin is 80,000 to 500,000, preferably 100,000 to 400,000. If the weight average molecular weight of the polypropylene resin is less than 80,000, the impact resistance of the obtained retort sealant film is not sufficiently given, and if the weight average molecular weight of the polypropylene resin exceeds 500,000, it is obtained. The flexibility of the sealant film for retort is impaired and the commercial value is reduced.

If desired, additives such as a heat stabilizer, an ultraviolet absorber, a slip agent and an anti-blocking agent may be added to the core layer and the sealant layer without departing from the spirit of the present invention.

The thickness of the sealant film for a retort according to the present invention is appropriately set depending on the type of food to be packaged and the amount of packaging, but the total thickness is 50 to 150 μm and the thickness of the sealant layer is about 5 to 60 μm. preferable. When the thickness of the sealant layer is less than 5 μm, the heat seal strength of the retort sealant film may be reduced, and when the thickness of the sealant layer exceeds 60 μm, the retort sealant film may have The impact strength may decrease.

The method for molding the sealant film for retort according to the present invention is not particularly limited.
By die extrusion molding method, inflation extrusion molding method,
The core layer and the sealant layer may be separately molded, and the both may be laminated using a laminating device such as a laminator. Alternatively, one of the core layer and the sealant layer may be molded and the dry film may be formed on the film. The layers may be laminated by a laminating method or an extrusion laminating method. Further, both layers of the core layer and the sealant layer may be laminated at once by a coextrusion molding method such as a T-die coextrusion molding method and an inflation coextrusion molding method. May be manufactured. In particular, according to the feed block co-extrusion molding method, an adhesive is not necessary, and a strong interlaminar strength of both layers of the retort sealant film is easily obtained, and therefore, the retort sealant film of the present invention is molded. Is a preferable molding method.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. (Examples 1 and 2) Polypropylene resin (P
P resin) and an ethylene-based elastomer (trade name: Tuffmer manufactured by Mitsui Petrochemical Co., Ltd.) were prepared by a resin composition for a sealant layer prepared by a mixing ratio and a mixing method shown in Table 1 and two kinds of monomers shown in Table 1. A polypropylene resin for a core layer, which is made of a reactor blend polymer (trade name: Catalloy, manufactured by Highmont Co., Ltd.) obtained by a multi-stage polymerization reaction, has a thickness shown in Table 1 and a sealant film for a retort by a laminating method shown in Table 1. Was produced. 12 μm thick single-sided corona discharge treated biaxially stretched polyester film dry laminated with urethane adhesive and thickness 1
The biaxially stretched polyamide film side of the 5 μm double-sided corona discharge treated biaxially stretched polyamide film composite film was laminated on the core layer side of the obtained retort sealant film to prepare a retort packaging film.

[0029]

[Table 1]

(Comparative Examples 1 to 3) A reactor blend obtained by a multi-step polymerization reaction of polypropylene resin (PP resin) and ethylene elastomer (all of the above) shown in Table 2 and two kinds of monomers shown in Table 2 The polymer was prepared according to the mixing ratio and the mixing method shown in Table 2, and in the same manner as in Example 1, a sealant film for retort was prepared with the thickness and the laminating method shown in Table 2. On the side of the core layer of the obtained sealant film for retort, as in Example 1, 2
A packaging film for a retort was produced by laminating a composite film composed of an axially stretched polyester film and a biaxially stretched polyamide film.

[0031]

[Table 2]

(Examples 3 to 4), (Comparative Example 4) A polypropylene resin (PP resin) and an ethylene elastomer (trade name: Tuffmer manufactured by Mitsui Petrochemical Co., Ltd.) shown in Table 3 are mixed as shown in Table 3. A resin composition for a sealant layer prepared by a ratio and a mixing method, a polypropylene resin and an ethylene elastomer shown in Table 3 (ethylene / 1-octene copolymer: manufactured by Dow Chemical Co., trade name "engage", ethylene / 1-butene copolymer: trade name "Toughmer" manufactured by Mitsui Petrochemical Co., Ltd.) was prepared according to the mixing ratio and mixing method shown in Table 2, and the resin composition for the core layer, the thickness and the lamination shown in Table 3 were obtained. A retort sealant film was produced by the method. A composite film composed of a biaxially stretched polyester film and a biaxially stretched polyamide film was laminated on the core layer side of the obtained retort sealant film in the same manner as in Example 1 to prepare a retort packaging film.

[0033]

[Table 3]

The following items were tested in order to evaluate the performance of the retort sealant film, using the packaging films for retorts obtained in the above Examples and Comparative Examples as samples. The test results are shown in Table 4.

1. Heat-seal saturation temperature: Two retort packaging films are put together on the sealant layer side and heat-sealed at a pressure of 2 kg / cm ² . Measure the seal strength per 15 mm width at a speed of 300 mm / min (T
The mold was peeled off) and the temperature at which the strength was saturated was measured as the heat seal saturation temperature.

2. Inner surface blocking property by retort treatment: Sealant layer sides of two retort packaging films are put together and heat-sealed at a temperature higher by 10 ° C. than the heat-sealing saturation temperature, vertical 20 cm × width 15 c
After making a bag of m, filling the bag with 150 g of commercially available beef curry and sealing the opening of the bag under the same conditions, 121 ° C ×
Perform retort treatment for 30 minutes. After the retort treatment, the bag is opened and the presence or absence of fusion between the sealant layers is observed,
◯: No blocking was observed anywhere, Δ: Light blocking was observed, but easily peeled off, ×: Strong blocking that could not be peeled off was evaluated.

3. Impact resistance evaluation: Drop the retort-treated pouch (filled with 150 g of beef curry) used in the blocking test of the previous section from a height of 1.5 m, and
The number of broken bags in 0 bags was counted.

[0038]

[Table 4]

[0039]

Since the retort sealant film of the present invention is constructed as described above, it is an excellent retort sealant film satisfying both impact resistance and low temperature sealability, and is a biaxially stretched polyester film. It is possible to provide a film for an excellent retort pouch that satisfies both impact resistance and low-temperature sealing property by combining with a biaxially stretched polyamide film or the like.

Claims (2)

[Claims] 1. A polypropylene resin in an amount of 10 to 70 parts by weight,
Random copolymerized polypropylene resin 70-
A sealant film for a retort, comprising a sealant layer composed of 90 parts by weight and 30 to 10 parts by weight of an ethylene elastomer. 2. The amount of elution in each temperature range by the cross fractionation method is 45 to 80% by weight at 10 ° C. or less based on the total weight,
5 to 45% by weight above 10 ° C and below 75 ° C, above 75 ° C to 95 ° C
0 to 20% by weight below, 5 to 3 above 95 ° C and below 125 ° C
5% by weight, 70-90 parts by weight of a random copolymerized polypropylene-based resin on one surface of a core layer made of a polypropylene-based resin having a weight average molecular weight in the range of 80,000-500,000,
A sealant film for a retort, which comprises laminating a sealant layer comprising 30 to 10 parts by weight of an ethylene elastomer.