JPS6160769B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [] BACKGROUND OF THE INVENTION The present invention relates to a laminated material that has improved heat resistance without reducing heat sealability. More specifically, the present invention relates to a laminated material suitable for use in containers for food products that are retortable, ie, heat sterilizable while filled. More specifically, the present invention relates to a laminated material suitable for use as a container that can withstand retort processing at significantly higher temperatures than conventional materials. BACKGROUND OF THE INVENTION Cooked food products, such as cooked rice, curry, soup, and grilled eel, are placed in various forms of retort containers such as pouches, trays, and cups, and are sold on the market as so-called retort foods. These retort containers have the strength to withstand retort processing at high temperatures and pressure (e.g., low deformation rate under heating and pressure, high sealing strength at the sealing part, etc.), and pressure shock resistance at high temperatures or room temperature. Although high gas barrier properties and light shielding properties are required to protect the contents from oxidative deterioration and deterioration due to ultraviolet rays, it is difficult to obtain a single material that has all of these properties at the same time. A method has been adopted in which a plurality of materials having the required performance are laminated and used. That is, the innermost layer is made of a material that is easy to seal, maintains the necessary strength even at retort processing temperatures, and can withstand pressure impact. Specifically, high-density or medium-density polyethylene is used when retort processing is required at relatively low temperatures (about 115 to 125 degrees Celsius); When retort treatment is assumed, polypropylene, a block copolymer of propylene and a small proportion of ethylene, or a mixture of polypropylene and ethylene-propylene copolymer rubber is often used. Metal foil and various gas barrier thermoplastic resins are used as materials with gas barrier and light shielding properties for the outer layer, and as needed, further outer layers are used to improve strength, printability, water vapor barrier properties, and other properties. A resin layer having the following characteristics is sometimes used. In between these two or three basic layers, there may be an adhesive layer or other layer for other purposes. By the way, improving the sterilizing effect of retort food,
In order to prevent the quality of the contents from deteriorating by shortening the processing time and to improve work efficiency, there is a need to develop container materials that can further increase the processing temperature (approximately 140 to 160°C). The most important requirement in this case is how to give the material used for the innermost layer a balance between high heat resistance and heat sealability, as well as pressure impact resistance when made into a container. Of course, it goes without saying that such a material must be industrially manufactured at low cost. [] Summary of the Invention The present invention aims to solve the above-mentioned problems, and uses a copolymer mainly consisting of propylene and 4-methylpentene-1 as a resin for a layer that provides heat-sealing properties to a laminated material. We attempt to achieve this objective by using coalescence. Therefore, the laminated material according to the present invention has a layer of a copolymer mainly composed of propylene and 4-methylpentene-1 and a metal foil or a layer having a gas permeability coefficient of 1×10 ^-10 (cm ³ STP) for oxygen gas at 30°C. )(cm)/
(cm ² ) (sec) (cmHg) or less. Effects When used as a heat-sealer for laminated materials, the copolymer mainly composed of propylene and 4-methylpentene-1 is soft and has high impact resistance, and has low-temperature heat-sealing properties close to that of polyethylene. It has the advantage that processing temperatures as high as 160°C are possible. [] Detailed description of the invention 1 Propylene/4-methylpentene-1 copolymer (1) Monomer species The resin used as the layer of the laminated material of the present invention to enable low-temperature heat sealing/high-temperature treatment is:
It is a copolymer mainly composed of propylene and 4-methylpentene-1. One specific example of this copolymer consists essentially only of these two comonomers. Another example of this copolymer is the combination of these two comonomers with ethylene and butene-1.
or (and) hexene-1. In the case of any of these copolymers, besides the comonomers mentioned, small amounts of other comonomers may also be copolymerized, provided that they do not significantly impair the resin properties achieved by this comonomer combination. Also within the scope of this invention are copolymers that include (2) Analysis by DSC In the present invention, the analysis of this copolymer and the selection of the optimal species are performed based on the melting curve obtained by DSC (differential scanning calorimetry). Note that the measurement by DSC was carried out at a heating rate of 10° C./min on a sample crystallized at a cooling rate of 10° C./min. The above-mentioned copolymer used in the present invention has, compared to the homopolymer of each monomer used,
As is clear from the melting curve by DSC,
It is a polydisperse copolymer that melts over a wide temperature range. This means that the total heat of fusion, Q ₀ [cal/g-copolymer), calculated from the melting curve, is the heat of fusion of the portion that melts below 150°C, Q (cal/g-copolymer), and
It is clear from the fact that the heat of fusion, Q (cal/g-copolymer), of the portion that melts at a temperature of 170° C. or higher preferably accounts for 3% or more and 3% or more, respectively. As will be described later, the ratios of Q and Q to Q ₀ can be made to exceed 90% and 90%, respectively, by varying the composition of the copolymer. It is easily estimated that Q and the size of Q are closely related to the factors for heat sealability and heat resistance development, respectively. The preferred range of the ratio of Q and Q to Q ₀ is 5, respectively.
~40% and 5-50%, with the most preferred ranges being 10-35% and 7-35%, respectively.
If Q is smaller than this, high temperature, high pressure, or a long time will be required when forming the laminated material into a container such as a pouch by heat sealing, which will not only worsen workability but also cause shrinkage in other resin layers used together. This is not preferable as it may result in destruction or other inconveniences. It also causes damage to the heat-sealed portion due to pressure impact during use. When the value of Q falls below the above range, the material loses its shape retention against stress at high temperatures, and loses its suitability as a material for high-temperature retort containers. Another feature of the physical properties of this copolymer is that
Its impact resistance is strong. It is known that both isotactic homopolymers of propylene and 4-methylpentene-1 are glassy at room temperature and brittle against impact. This polymer is obtained by copolymerizing both of them using various methods to change the above-mentioned melting characteristics and at the same time improve impact resistance. Furthermore, ethylene, butene-1 or hexene-1 may be added to these two comonomers as necessary.
It has also been found that by using a third comonomer selected from the above, it is possible to further improve impact resistance while maintaining the melting properties necessary to maintain the heat sealability and heat resistance mentioned above. . (3) Copolymerization (1) Catalyst The present copolymer is usually produced by a one-stage or multi-stage polymerization method using a Ziegler type catalyst. As the Ziegler type catalyst, any catalyst that can stereoregularly polymerize propylene and 4-methylpentene-1 alone can be used, but preferably a catalyst containing a titanium compound and an organoaluminum compound as the main components is used. It will be done. Specifically, α, β,
Various types of γ- and δ-type titanium trichloride, and titanium trichloride or titanium tetrachloride supported on various carriers mainly composed of magnesium chloride, are combined with diethylaluminium chloride, triethylaluminum, and other organoaluminiums. Create a catalyst system. In this case, it is also possible to enhance activity and other catalyst performance by adding various electron-donating compounds to the catalyst system. Among these catalyst systems, aluminum chloride is extracted and removed using a complexing agent from a eutectic composite of titanium trichloride and aluminum chloride, which is obtained by reducing titanium tetrachloride using organoaluminium. A catalyst system in which a titanium chloride composition is combined with diethylaluminum chloride has the ability to increase the reactivity of 4-methylpentene-1, which is relatively poor with respect to propylene, compared to other catalyst systems, and the co-formation It can be said to be one of the most preferred polymers because of its excellent particle properties (particularly high bulk specific gravity). (2) Polymerization method When carrying out copolymerization in one step, the following method can be adopted. (b) Under a constant pressure of propylene (and a mixed gas with ethylene or butene-1 if necessary), a predetermined amount of 4-methylpentene-1 and, if necessary, hexene-1, is added all at once at the time of polymerization initiation. At a constant rate over the entire time range or intermittently divided over the entire polymerization time range,
Batch method for charging into reaction tanks. (b) While charging propylene (and ethylene or butene-1 if necessary) at a constant rate until the specified pressure is reached, 4-methylpentene-1 and if necessary hexene-1
1 is a batch method in which a predetermined amount is charged at once at the start of polymerization at a constant rate over the entire polymerization time range, or intermittently divided over the entire polymerization time range and charged into the reaction tank. (c) Propylene (and ethylene or butene-1 if necessary) is charged into the reaction tank so that the total pressure and partial pressure are kept constant, while 4-methylpentene-1 and if necessary hexene-1 are supplied at a constant rate. Continuous method. When copolymerization is carried out in multiple stages, the following method is adopted. (d) After carrying out the homopolymerization of propylene, while continuing to supply propylene,
Alternatively, immediately after stopping the supply of propylene, or when the partial pressure of propylene has decreased to a predetermined pressure, 4-methylpentene-1
Batch method that supplies hexene-1 as needed. (e) A batch method in which a mixed monomer of propylene and ethylene or butene-1 is used instead of the propylene in (d) above, and the other steps are the same as in (d). (f) A batch method in which a propylene homopolymerization step is added to the previous step of (e) above, and the other steps are the same as in (e). (G) A continuous method in which the various polymerization steps in (d) to (f) of the above batch method are carried out simultaneously in a plurality of consecutive reaction vessels. Although the above is just a few typical examples for obtaining the copolymer of the present invention, it goes without saying that any other practicable method may be employed. Preferred copolymers (Q/Q ₀ ≧3%,
Q/Q ₀ ≧3%) it is necessary to vary the concentration of the comonomer relative to propylene over time. For example, it is preferable to feed all comonomers other than propylene and feed propylene at a constant rate. (4) Preferred copolymer In order for the copolymer produced by the above polymerization method to have the desired properties, the content of 4-methylpentene-1 unit in the copolymer must be 2 to 90%. , preferably 5 to 70% by weight, most preferably 10 to 60% by weight. If the content is lower than this, Q will not be able to reach the required level, and therefore heat resistance will not be sufficiently exhibited. On the other hand, if the content is higher than this, the heat resistance itself will not be a problem, but the proportion of the low melting point copolymer will decrease.
cannot be of a given magnitude, and Q and Q
In other words, it becomes impossible to maintain the balance between heat sealability and heat resistance.
As mentioned above, preferred copolymers include DSC
Calculated based on the melting curve obtained by
Heat of fusion Q of the part that melts below 150℃
The heat of fusion Q of the part that melts at 170℃ or higher is 3% or more of the total heat of fusion Q ₀ and 3, respectively.
% or more. The use of ethylene, butene-1 or hexene-1 as the third monomer is not an essential requirement, but is very effective in improving impact resistance and heat sealing without significantly compromising heat resistance. The proportion of these third monomers in the copolymer is usually 7% by weight or less, preferably 4% by weight or less.
% by weight or less. If the amount is more than this, the heat resistance of the copolymer will deteriorate, which is not preferable. The copolymer mainly composed of propylene and 4-methylpentene-1, which is a requirement of the present invention, is considered to be an aggregate of many chains in which the monomer composition and distribution in each copolymer chain varies over a wide range. However, a large proportion of the chains giving a high melting point are 4
The chains which are composed of 1-methylpentene and a small proportion of propylene and which give a low melting point will be mainly composed of a large proportion of propylene and a small proportion of 4-methylpentene-1. Here, ethylene as the third monomer,
When butene-1 or hexene-1 is used in combination, heat sealability and impact resistance are improved without significantly impairing heat resistance. This is probably because the crystallinity associated with this chain is lowered more selectively by the introduction of the chain (note that the present invention is not bound by such a theory). 2 Gas barrier layer Propylene and 4-methylpentene-1 (ethylene, butene-1 or hexene-1 as necessary)
The resin to be used for the gas barrier resin layer to be used in combination with the copolymer layer of 1 and) has a gas permeability coefficient P for oxygen gas of 1×10 ^-10 at 30°C.
(cm ³ STP) (cm) / (cm ² ) (seconds) (cmHg) or less. The value of P is 1 cm ² in cross section,
When a resin layer with a thickness of 1 cm is separated and oxygen gas is present at a differential pressure of 1 cmHg, the amount of oxygen gas that substantially permeates through this resin layer in the direction of the differential pressure in one second is 0.
℃, means the volume converted to 1 atm. The preferred value of P in the present invention is 0.5×10 ^-10 (cm ³
STP) (cm)/(cm ² ) (sec) (cmHg) or less, more preferably 0.1×10 ^-10 (cm ³ STP) (cm)/
(cm ² ) (seconds) (cmHg) or less. edited by J.Brandrup and EHImmergutpolymer
Handbook, Interscience Publishers;
New York, London, Sydney (1967) No.
According to page 13, the following are listed as examples of resins that meet these conditions (p×
10 ^-10 , temperature). Cellulose (0.0021, 25℃),
Amorphous poly(trifluorochloroethylene)
(0.038, 30℃), crystalline poly(trifluorochloroethylene) (0.045, 30℃), polyformaldehyde (0.38, 30℃), polyvinyl acetate (0.5, 30℃), polyvinyl alcohol (0.0089, 25℃) , polyvinyl chloride (0.0453, 25
°C) and polyvinylidene chloride (0.0053, 30
℃). Journal of Membrane Science, 2
(1977) 153-164 (SMAllen, M.Fujii, V.
Stanett, H.B. Hopfenberg and J.L.
Williams) also has polyacrylonitrile (0.0003,
30℃), polymethacrylonitrile (0.0012, 30
°C), "Lopac" (acrylonitrile copolymer from Monsanto Co. 0.0035, 30 °C), "Barex"
(Acrylonitrile resin manufactured by Sohio Co.
0.0054, 30℃), and polyethylene terephthalate (0.035, 30℃) as an example of polyester resin.
°C), nylon 6 as an example of polyamide resin
(0.038, 30℃), respectively. In addition to these, saponified ethylene-vinyl acetate copolymers with an ethylene content of 25 to 50 mol% and a degree of saponification of 96% or more, polycarbonates, copolymers of vinyl chloride and vinylidene chloride, and It is known that copolymers of acrylonitrile or methacrylonitrile and styrene, vinyl acetate, or acrylic esters containing mol% or more also have certain oxygen barrier properties. All of these resins are suitable for use as components of the laminated material of the present invention, but
Particularly preferred are polyester, polyamide, polycarbonate, polyvinyl chloride, polyvinylidene chloride, vinyl chloride-vinylidene chloride copolymer, and ethylene-vinyl acetate with an ethylene content of 25 to 50 mol% and a saponification degree of 96% or more. Saponified copolymers, homopolymers of acrylonitrile or methacrylonitrile containing 5 mol % or more of acrylonitrile or methacrylonitrile units, or copolymers of these monomers with styrene, vinyl acetate or acrylic ester. Another group of barrier layers are metal foils that have both light blocking and gas barrier properties. Aluminum foil is a typical metal foil, but the use of iron foil has also begun to be considered in recent years. Other metal foils may also be used in the laminate materials of the present invention, as economics permitting. 3 Lamination In the laminated material according to the present invention, the propylene/
The 4-methylpentene-1 copolymer A is used for the heat-sealing layer or the first layer (innermost layer), and the metal foil or gas barrier resin material B is used for the layers other than the first layer. There may be a plurality of each layer as necessary. Note that various adhesive layers used as necessary between each layer are not counted as constituent layers of the laminated material in the present invention, even if they are resin layers. Even if this adhesive layer achieves a non-adhesive effect, or even if a decorative layer or other layer is provided, the laminated material with such a layer must be combined with a layer of copolymer A and a metal foil or gas barrier. It is within the scope of the present invention, characterized in that it includes a synthetic resin material B. Also,
When referring to a layer of copolymer A, this copolymer A
It is also intended to include layers consisting of a mixture of and a kneadable small amount of a compatible resin. It is convenient to classify the laminated material of the present invention into two-layered materials, three-layered materials, and four or more layered materials depending on the number of layers constituting the laminated materials. In particular, two-layer and three-layer materials are the most important in practical terms, followed by four-layer and five-layer materials, which become less important in that order. Typical lamination styles are shown below. (1) Two-layer material (a) First layer (innermost layer) - Copolymer A Second layer (outermost layer) - Metal foil (b) First layer - Copolymer A Second layer - Gas barrier resin B However, among the gas barrier resins B in this case, those whose gas barrier properties are significantly impaired by moisture absorption have no practical meaning. Examples of such resins include those containing a large amount of hydroxyl groups in the molecule, typical examples of which are cellulose resins and vinyl alcohol resins. The barrier properties of nitrile resins and polyamides also decrease slightly due to moisture absorption, but this does not pose a problem in practice. (2) Three-layer material (a) First layer (innermost layer) - Copolymer A Second layer (middle layer) - Metal foil Third layer (outermost layer) - Thermoplastic resin Third layer resin used here is a layer whose purpose is to protect the second layer of metal foil, maintain the strength of the entire laminated material, print, etc. Since the metal foil in the middle layer has gas barrier properties, this third layer does not necessarily have gas barrier properties. There is no need to have one. Therefore, such thermoplastic resins include not only copolymer A that can be used for the first layer, but also polyolefin resins such as polypropylene and polyethylene, other resins, and various thermoplastics exemplified as gas barrier resin B. You can choose from resins. (b) First layer - Copolymer A Second layer - Gas barrier resin B Third layer - Thermoplastic resin In this case, gas barrier resin B is used as an intermediate layer, and is separated from both sides by separate layers. Since it is protected, it can fully exhibit its function even if its gas barrier properties are degraded due to moisture absorption, unlike the case of the outermost layer of a two-layer material.
In other words, when a gas barrier material containing a large amount of hydroxyl groups is used for the second layer, the thermoplastic resin used for the third layer needs to have low permeability to moisture. Specifically, the water vapor permeability coefficient at 30℃ is 1000.
×10 ^-10 (cm ³ STP) (cm) / (cm ² ) (sec) (cm
Hg) or less is a guideline for selection. Resins that satisfy these conditions include polyolefins, halogenated hydrocarbon polymers,
Examples include polyamides, polyesters, nitrile group-containing polymers, and the like. The laminated material as described above is manufactured by various molding methods, but dry lamination processing is typically used. Other methods include extrusion coating, coextrusion, and coextrusion coating, and combinations of these may also be employed. If necessary, an adhesive layer or an anchor coat layer can be provided between the layers to improve the interlayer adhesive strength. The thickness of the layer of copolymer A in the laminated material of the present invention is:
From the perspective of ensuring the required seal strength, 10~
It is usually about 200μ, preferably about 30 to 100μ. The thickness of the layer of gas barrier resin material B may be determined from the viewpoint of ensuring the required oxygen barrier properties, and is usually about 5 to 30 microns.
In addition, in a deep-drawn container etc. in which aluminum foil is used as a gas barrier layer as shown in Example 5 of the present invention, the aluminum foil not only functions as a gas barrier layer but also functions to impart shape retention to the container itself. 50 to 300μ in such cases.
It needs to be as thick as possible. 4 Experimental Examples Example 1 Content of 4-methylpentene-1 unit is 32% by weight, the peak positions of the melting curve by DSC are at 156°C and 220°C, and the melting temperature is below 150°C calculated based on the melting curve. Heat of fusion of the part and 170
Propylene and 4-, whose heat of fusion of the part that melts above ℃ are 12% and 25% of the total heat of fusion, respectively.
Using a random copolymer with methylpentene-1 (MFR4g/10min), the first layer is a 60μ thick film that is T-die cast molded and corona treated on one side by a conventional method, and a 9μ thick aluminum foil is used as the first layer. The second layer was a biaxially stretched polyethylene terephthalate film (Diaphoil manufactured by Mitsubishi Plastics Co., Ltd.) having a thickness of 12 μm as the third layer, and a laminated film was prepared by a known dry lamination process. The adhesion between each layer was achieved by applying a polyurethane-isocyanate adhesive (ADCOTE 503H manufactured by Toyo Morton Co., Ltd.) and "Catalyst F" to a solid content of 10 g/m ² using a gravure coating method. Cut two rectangular pieces of 130 mm x 170 mm from this laminate, place the first layer facing each other, and heat the two vertical sides and one horizontal side with a width of 10 mm at 200°C, 3 Kg/cm ² , and 2.0 seconds. It was sealed and made into a bag. heat seal part
The 180° seal strength was measured at a width of 20 mm and a tensile speed of 500 mm/min. Next, add 100g of commercially prepared curry to this bag.
was inserted, and the opening was heat-sealed under the above conditions.
This was placed in a hot water retort can and subjected to retort treatment under predetermined conditions of temperature and time. After processing, the bags containing their contents were placed horizontally and dropped from a height of 1.5 m, and the number of bags that could no longer maintain a sealed structure due to pinholes, breakage, etc. was measured (test sample number). 25 bags). On the other hand, a heat-sealed portion was cut out from a bag after retort processing that was not subjected to the drop bag tear test, and the seal strength was measured under the same conditions as above. The measurement results are shown in Table 1. Comparative Example 1 A laminated film was prepared and its suitability as a retort pouch was evaluated under the same conditions as in Example 1, except that an isotactic polypropylene film was used instead of the copolymer film of propylene and 4-methylpentene-1. We conducted an evaluation. The results are shown in Table 1. Example 2 The content of 4-methylpentene-1 unit was 2% by weight, and the peak position of the melting curve by DSC was 150°C.
The heat of fusion of the part that melts below 150℃ calculated based on the melting curve and
A film consisting of a random copolymer of propylene and 4-methylpentene-1 (MER4) whose heat of fusion in the portion that melts at 170°C or above is 54% and 0% of the total heat of fusion, respectively, is used as the first layer. A three-layer laminated film was prepared and its suitability as a retort pouch was evaluated under the same conditions as in Example 1, except for the following conditions. The results are shown in Table 1. Example 3 The first layer consisted of a film of the same propylene and 4-methylpentene-1 copolymer used in Example 1, and the second layer consisted of a 15μ thick saponified copolymer of ethylene and vinyl acetate. Using the same biaxially oriented polyethylene terephthalate film as used in Example 1 as the third layer of the film ("EVAL" film manufactured by Kuraray Co., Ltd.), a laminated film and a bag using the same were created in the same manner as in Example 1, Similar to Example 1, suitability as a retort pouch was evaluated. The results are shown in Table 2. Comparative Example 2 A laminated film was prepared under the same conditions as in Example, except that an isotactic polypropylene film was used instead of a copolymer film of propylene and 4-methylpentene-1, and its suitability as a retort pouch was evaluated. I did this. The results are shown in Table 2. Example 4 The first layer was the same copolymer film of propylene and 4-methylpentene-1 used in Example 1, and the third layer was a biaxially stretched nylon film with a thickness of 15 μm (“Emblem” film manufactured by Unitika).
A two-layer laminated film was prepared by dry lamination in the same manner as in Example 1, and its suitability as a retort pouch was evaluated. The results are shown in Table 2. Comparative Example 3 A laminated film was prepared under the same conditions as in Example 4, except that an isotactic polypropylene film was used instead of the copolymer film of propylene and 4-methylpentene-1, and its suitability as a retort pouch was determined. We conducted an evaluation. The results are shown in Table 2. Example 5 As the first layer, the same copolymer film of propylene and 4-methylpentene-1 as used in Example 1 was used, and as the second layer, aluminum foil with thicknesses of 12μ and 100μ was used, and the same as in Example 1. A laminated film was created using this method. A laminate of aluminum foil with a thickness of 100 μm was formed into a deep-drawn container with a depth of 15 mm and an opening of 100 mm×150 mm by drawing, with the aluminum layer facing outside. Put 100g of commercially available cooked curry into this container, then add aluminum foil with a thickness of 12μ to this container.
The laminates were stacked so that the resin layers were facing each other, and heated at 200°C with a width of 10 mm along the periphery of the concave part of the container at 3 kg/kg.
Heat sealing was performed under the conditions of cm ² and 2.0 seconds. This was subjected to retort treatment and evaluation of retort container suitability under the same conditions as in Example 1. However, during the drop test, the container was dropped with the lid side down to make it easier to break. In addition, the seal strength of the heat-sealed portion before and after retort processing is determined by pinching the heat-sealed portion and peeling it off from the side opposite to the periphery of the recess, since the test piece is curved around the periphery of the container recess, which causes variation in data. It was measured. The results are shown in Table 3. Comparative Example 4 A laminated film was prepared under the same conditions as in Example 5, and its suitability as a retort container, except that an isotactic polypropylene film was used instead of the propylene and 4-methylpentene-1 copolymer film. We conducted an evaluation. The results are shown in Table 3. [Table] [Table] [Table]

Claims (1)

[Claims] 1 Copolymer layer consisting mainly of propylene and 4-methylpentene-1 and metal foil or gas permeability coefficient for oxygen gas at 30°C is 1 × 10 ^-10
(cm ³ STP) (cm)/(cm ² ) (sec) (cmHg) or less, a layer of a gas barrier resin material.