JPH0128065B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a laminate, which has simple steps and excellent productivity, and which aims to improve moldability, retort resistance, food resistance, and chemical resistance. Conventionally, for bags or containers used for retort sterilization, aluminum foil and polypropylene film or high-density polyethylene film bonded together using a two-component thermosetting urethane adhesive have been used as the inner layer that comes into contact with food. ing.
However, such a device has many drawbacks as follows. That is, since it is a two-component thermosetting adhesive, it requires aging to accelerate the reaction, and special care and time are required to set the conditions. If the adhesive is aged for a long time at a high temperature in order to obtain sufficient performance, the polypropylene film or high-density polyethylene film will harden and its moldability will deteriorate. Even if proper aging is performed in consideration of many factors, the performance of the adhesive may not be fully demonstrated.
Retort sterilization tends to cause delamination. As for food resistance, it has insufficient durability against highly acidic foods, oily foods, seasonings, spices, and the like. etc. Recently, in order to improve the drawbacks when using such two-component curing adhesives, a modified polypropylene resin modified with an unsaturated carboxylic acid or its acid anhydride is used as the adhesive layer, and aluminum foil A method has been proposed for thermally bonding a polypropylene film and a polypropylene film, but this method eliminates the need for a heat forming process and provides a laminate with excellent retort resistance, moldability, and food resistance. However, it has the following drawbacks in terms of productivity, and has not been put into practical use. That is, in order to sufficiently bond the modified polypropylene resin to the aluminum foil, it is necessary to heat it at high temperature for a long time, which leads to a decrease in production speed and an increase in energy consumption. When extruding and thermally bonding a layer of heat-molten modified polypropylene resin between an aluminum foil and a preformed polypropylene film, or when bonding a modified polypropylene resin and a polypropylene resin on top of an aluminum foil in two layers, When coextruding layers and thermally bonding them, if the temperature of the molten resin is raised to a high temperature in order to improve the adhesiveness with the aluminum foil, the modified polypropylene resin will undergo thermal deterioration and will no longer adhere to the aluminum foil at all. In order to prevent this phenomenon, the temperature of the molten resin must be lowered, but lowering the temperature deteriorates the adhesion to the aluminum foil. Therefore, methods such as heating the base material in advance or heating the laminate after lamination may be considered, but this would lead to a decrease in productivity. Even when thermally bonding aluminum foil and a pre-formed coextruded film of modified polypropylene and polypropylene between hot rolls, if the temperature of the hot roll is raised to a high temperature, the polypropylene softens and adheres to the roll. Because of this, it is necessary to reduce the operating speed at a low temperature that does not soften the polypropylene.
This will lead to a decrease in productivity. The thickness of the modified polypropylene layer cannot be reduced by hot melt extrusion, and the layer thickness inevitably becomes 15 μm or more. Therefore, the present invention was made to eliminate all of the conventional drawbacks (i.e., the above), and involves applying an organic solvent dispersion or an aqueous dispersion of a modified polyolefin resin to an aluminum foil or sheet, In the method for producing a laminate, which comprises heating and drying to form an adhesive layer with a thickness of 0.1 to 10 μm, and then thermally bonding a polypropylene resin layer, a polyethylene resin layer, or a blend layer of these two, The modified polyolefin resin contains 3 to 97 parts by weight of a modified polypropylene resin modified with an unsaturated carboxylic acid or its acid anhydride, and 97 to 3 parts by weight of a modified polyethylene resin modified with an unsaturated carboxylic acid or its acid anhydride. The present invention provides a method for producing a laminate that can be sterilized by retort, characterized by heating and drying at a drying temperature of 140 to 180°C, and details thereof will be described below. First, in the present invention, the modified polypropylene resin of the modified polyolefin resin that forms the adhesive layer is obtained by graft copolymerizing an unsaturated carboxylic acid or its acid anhydride to introduce a carboxyl group into the polypropylene resin. The acid value, which is a measure of the amount of acid introduced, is
The content is preferably 0.1 to 100 mgKOH/g. This is because if the acid value is less than 0.1, the adhesive strength with aluminum foil will be poor, and if it exceeds 100, the adhesive strength with polypropylene resin will decrease. The polypropylene resin used as the raw material here can be a propylene homopolymer or a crystalline propylene-ethylene copolymer with a propylene content of 80 mol% or more, and the unsaturated carboxylic acid or its acid anhydride can be maleic acid, Examples include fumaric acid, crotonic acid, acrylic acid, methacrylic acid, maleic anhydride, and itaconic anhydride.
Such modified polypropylene resin has strong adhesion to aluminum foil and polypropylene resin, and has properties inherent to polypropylene resin, so it has excellent heat resistance, retort resistance, food resistance, and chemical resistance. It brings about excellent effects. Next, another modified polyethylene resin is
Similar to the modified polypropylene resin, a carboxyl group is introduced into a medium-density or high-density polyethylene resin by graft copolymerizing an unsaturated carboxylic acid or its acid anhydride,
The acid value, which is a measure of the amount of acid introduced, is 0.1 to 100 mg.
Preferably it is KOH/g. because,
This is because if the acid value is less than 0.1, the adhesive strength with aluminum foil will be poor, and if it exceeds 100, the adhesive strength with polyethylene resin will decrease. As the raw material polyethylene resin here, medium density or high density polyethylene is advantageously used, and crystalline ethylene-propylene copolymers having an ethylene content of 80 mol% or more can also be used. By using such a modified polyethylene resin, it has the effect of strongly adhering to aluminum foil and polyethylene resin, and has a lower melting point than the modified polypropylene resin, which has the effect of lowering the heating temperature when forming the adhesive layer. can get. In other words, the resin particles soften and flow at a lower temperature than when using modified polypropylene alone to form a uniform coating film, and furthermore, when thermocompression bonded to polypropylene, polyethylene film, or a blend film of the two, It also has the effect of being able to bond at a lower temperature, and does not impede the retort resistance, food resistance, chemical resistance, etc. of modified polypropylene. The compatibility of such modified polypropylene resin and modified polyethylene resin in the coating film after heat drying is good, and it does not become brittle like a blend of polypropylene resin and polyethylene resin. This is thought to be due to the fact that the interfacial adhesive force between the modified polypropylene resin and the modified polyethylene resin is superior to that between the unmodified polypropylene resin and the polyethylene resin. Here, the blending ratio of the modified polypropylene resin and the modified polyethylene resin is determined from the viewpoints of adhesion between the polypropylene resin and the polyethylene resin and low-temperature thermocompression bonding properties, to 3 to 97 parts by weight of the modified polypropylene resin and 97 parts by weight of the modified polyethylene resin. ~3 parts by weight is good, preferably 80 to 20 parts by weight of the modified polyethylene resin to 20 to 80 parts by weight of the modified polypropylene resin. This is because when the modified polypropylene resin is less than 3, the adhesion to polypropylene becomes poor.
This is because if it exceeds 97, the adhesion to polyethylene becomes poor and the effects of low temperature heat drying and low temperature thermocompression bonding properties provided by the modified polyethylene resin are lost. Note that the blending ratio (parts by weight) of modified polypropylene resin (abbreviated as P) and modified polyethylene (abbreviated as E) is preferably set as the following guideline depending on the objects to be bonded. That is, ● Especially in the case of polyethylene and polyethylene/polypropylene blends, P:E=(3-20):
(97~80) ●Especially when using polypropylene and polypropylene/polyethylene blends, P:E=(80~
97): (20~3) ●Other general polypropylene, polyethylene,
and a blend of these two, P:E
= (20~80): (80~20). However, instead of blending a modified polypropylene resin that has been modified in advance and a modified polyethylene resin, after blending an unmodified polypropylene resin and a polyethylene resin,
It goes without saying that one in which the carboxyl group content is adjusted to the above-mentioned value may be used. Furthermore, in order to provide such modified polyolefin resin with thermal adhesion and film forming properties at lower temperatures, it is necessary to soften and flow at a temperature lower than the melting temperature of the modified polyolefin resin and to make it compatible with polypropylene and polyethylene. It is effective to add 30% by weight or less of a resin that has good adhesion to aluminum foil, polypropylene, polyethylene, etc., ie, polypropylene and its derivatives, or polyethylene and its derivatives. If it exceeds 30% by weight, retort resistance and heat resistance will deteriorate, which is undesirable. Here, polypropylene and its derivatives have a molecular weight of 1000 to 12000.
low molecular weight polypropylene, chlorinated polypropylene, chlorinated carboxylated polypropylene (chlorinated modified polypropylene modified with an unsaturated carboxylic acid or its anhydride), etc. Polyethylene and its derivatives are
Low molecular weight polyethylene of about 1000 to 12000, ethylene-vinyl acetate copolymer, partially saponified ethylene-vinyl acetate copolymer, carboxylated ethylene
Vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-isobutyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-propylene rubber, ionomer, chlorinated polyethylene, chlorine and carboxylated polyethylene (chlorinated modified polyethylene modified with an unsaturated carboxylic acid or its anhydride). To make the organic solvent dispersion of the modified polyolefin resin described above, the modified polyolefin resin is
Either dissolve the resin in an organic solvent by heating it under normal pressure or increased pressure, and cool it while stirring well to precipitate fine resin particles, or crush the modified polyolefin resin in advance and disperse it in the organic solvent. You may let them. The organic solvent used is preferably one that dissolves the modified polyolefin resin at high temperatures, does not substantially dissolve it at room temperature, and is inert to carboxylic acids, such as toluene, xylene, cyclohexane, methylcyclohexane, hexane,
Heptane, mineral spirits, deodorized kerosene,
Examples include carbon tetrachloride alone or a mixture thereof. Moreover, in order to make an aqueous dispersion, after dissolving the modified polyolefin resin in the organic solvent, an alkaline aqueous solution may be added to form a dispersion, and the organic solvent may be removed. The organic solvent dispersion or aqueous dispersion of the modified polyolefin resin thus obtained is applied to an aluminum foil or sheet to form an adhesive layer using a conventional method such as roll coating or gravure coating. However, when applying a hot melt, it has a high viscosity that makes it difficult to wet aluminum foil or sheet and makes it difficult to adhere.
It is extremely difficult to form a thin layer of aluminum foil or sheet, but when an organic solvent or aqueous dispersion is used as in this invention, it has excellent wetting to aluminum foil or sheet and has good adhesion.
Therefore, a uniform layer with a thickness of 0.1 to 10 μm can be easily obtained, which is extremely advantageous economically. Here, if the layer thickness is less than 0.1μ, the adhesive strength is insufficient;
If it exceeds this, there will be no problem with adhesive strength, moldability, retort resistance, food resistance, etc.
10μ or less (especially 0.5~
5.0 μ) is practically desirable. Next, when drying the layer coated with such a modified polyolefin resin, the resin is heated to a temperature at which it softens and flows to volatilize the solvent and at the same time cause the dispersed resin particles to separate from each other. It is important to fuse and form a uniform coating film. Therefore, depending on the thickness of the aluminum foil or sheet, it must be heated and dried at 140 to 180°C, preferably 150 to 160°C, for 5 to 60 seconds, preferably 10 to 30 seconds. It won't happen. This is because low-temperature drying below 140°C does not improve adhesive strength sufficiently.
On the other hand, at high temperatures exceeding 180°C, the modified polyethylene undergoes thermal deterioration, resulting in a significant decrease in adhesive strength, making retort sterilization impossible. In addition, if such conditions are used, there is no need to knead at high temperatures for a long time as in the case of melt extrusion, so the risk of deterioration of the modified polyolefin resin can be completely avoided. The aluminum foil or sheet used in this invention is generally 20 to 500 μ thick for press-molded containers, and 6 to 80 μ thick for bag-like flexible sealed packages. These surfaces may be untreated or surface-treated by a method known per se, and bonded by applying a dispersion of the modified polyolefin resin. Usually, a solution of epoxy resin, acrylic resin, urethane resin, polyester resin, phenolic resin, urea resin, etc. is applied and baked on the side opposite to the side on which the agent layer is to be provided, or a solution of polyester, nylon 6, nylon 66, polycarbonate, etc. is applied and baked. The heat-resistant resin layer is formed by bonding films with good heat resistance such as 100% polyurethane using a polyurethane adhesive. The resin layer that is thermally bonded to the aluminum foil or sheet via the adhesive layer made of the modified polyolefin resin of this invention is made of polypropylene resin (homopolymer and medium density or high density polyethylene resins (including homopolymers and crystalline ethylene-propylene copolymers containing 80 mol% or more of ethylene);
Alternatively, a layer made of a blend of these two is preferable, and such a resin layer has good properties not only in heat sealing properties but also in terms of moldability required when used in molded containers, etc. , satisfactory results are obtained. In the method for manufacturing a laminate of the present invention described above, a resin layer with a thickness of 0.1 to 10 μm is formed by applying an organic solvent or aqueous dispersion of a modified polyolefin resin to an aluminum foil or sheet, and drying by heating. The lamination operation itself is generally carried out by known methods, i.e., extrusion lamination, extrusion coating, heat, etc., except that aluminum foil or sheet, etc., and the crystalline polyolefin resin layer are thermally bonded together using the aluminum foil or sheet as an adhesive layer. Any method such as lamination can be used. For example, as shown in FIG. 1, a dispersion 2 of modified polyolefin resin is applied to one side of an aluminum foil or sheet 1 by a roll coating method, and then heated and dried in a heating drying oven. 3
Before the adhesive layer obtained by heating and drying is cooled, an extruder 4 is used to apply a polyolefin resin onto the adhesive layer at a resin temperature of, for example, 240 to 290°C.
It is extruded into layers to form a laminate. This has the advantage that the heat used for heating and drying can be used effectively for thermal bonding. Further, as shown in FIG. 2, after forming an adhesive layer in the same manner as in FIG. ) and the rubber roll 8 for thermal bonding. Although there is no particular need for post-heating in either of these two methods, if post-heating is performed, it is possible to further increase the adhesive strength. In both the examples shown in Figures 1 and 2, the coating and drying of the modified polyolefin resin dispersion and the thermal bonding of the polyolefin resin layer were performed in-line. Needless to say, it is also possible to perform the process by an offline method, and since the adhesive layer of the present invention has almost no blocking property, aluminum foil on which the adhesive layer is formed without thermally bonding the polyolefin resin layer is used. Alternatively, even if the sheets are rolled up or stacked and stored under pressure, the blocking phenomenon does not easily occur. Note that the heat source of the heating and drying oven 3 may be any one of hot air, infrared heater, high frequency induction heating, etc., and a heating drum may be used. In addition to the normal method of thermal bonding,
A method of heating aluminum foil or sheet by high frequency induction heating can also be used. To summarize what has been said above, the present invention is capable of lowering the drying temperature by selecting modified polyolefins to be blended in a specific ratio, which is much more than what can be achieved by simply using modified polyolefins. You will be able to obtain the following effects that were previously impossible. That is, even though it is blended and dried at low temperatures, a uniform coating film with good compatibility can be obtained. Good low-temperature adhesion to polypropylene films, etc. Since it is a blend, it adheres to both polypropylene and polyethylene. It dries at a low temperature, and because of its low-temperature adhesion properties, the modified polyolefin does not undergo thermal deterioration, and because it is blended with modified polypropylene, it is heat resistant, and therefore, the combination of polypropylene and polyethylene is such that retort sterilization is possible. A strong adhesive force can be obtained between the two. etc. Examples and comparative examples are shown below. Example 1 Acid value 5 mgKOH/g modified with maleic anhydride
70 parts by weight of a modified polypropylene resin and 30 parts by weight of a modified high-density polyethylene resin modified with maleic anhydride and having an acid value of 5 mg KOH/g were dispersed in deodorized kerosene to form a 15% solution. Apply this solution by roll coating to the opposite side of a 90μ thick soft aluminum foil coated with heat-resistant epoxy resin on one side.
It was dried at ℃ for 15 seconds to form a 1.5μ thick adhesive resin layer. On the aluminum foil adhesive layer, a polypropylene resin having a melt index of 20 was extruded by a T-die method at a resin temperature of 290° C. to cover the adhesive layer with a thickness of 50 μm. Peel strength (T
Peeling) was 900g/15mm width. At this 120℃
Peel strength after 30 minutes of retort sterilization is 1100g/
It was 15mm wide. Such a laminate was formed into the shape of a container by cold press molding, filled with sweet and sour pork stock, heat-sealed with a lid, and retort sterilized at 120°C for 30 minutes, but the peeling and contents disappeared. There were no leaks at all, and the results were very good. Example 2 90μ adhesive layer formed in the same manner as Example 1
The adhesive layer side of a thick soft aluminum foil and a 50μ thick film made by blending 10% high-density polyethylene resin with pre-formed polypropylene resin are placed between a steel roll and a rubber roll heated to 150℃. I hot glued it through. The peel strength of this product was 850 g/15 mm width, and the strength after retort sterilization at 120°C for 30 minutes was 1050 g/15 mm width, which was an extremely good result. Example 3 90μ adhesive layer formed in the same manner as Example 1
The adhesive layer side of the thick soft aluminum foil and the modified polypropylene side of the preformed coextruded film of modified polypropylene (15 μ thick) and polypropylene (35 μ thick) were placed between a heating roll at 150°C and a rubber roll. It was heat-compressed. The peel strength of this product was 900 g/15 mm width, and the strength after retort sterilization at 120°C for 30 minutes was 1200 g/15 mm width. Example 4 90μ adhesive layer formed in the same manner as Example 1
Two layers of modified polypropylene (10μ) and polypropylene (40μ) were coextruded and laminated on a thick soft aluminum foil adhesive layer at a resin temperature of 260°C. The peel strength of this product is 800g/15mm width, and the strength after retort sterilization at 120℃ for 30 minutes is 1050
g/15mm width. Example 5 Acid value 0.1 or 10 mg modified with maleic anhydride
85 parts by weight of modified high-density polyethylene resin with KOH/g and acid value 0.1 or
15 parts by weight of modified polypropylene resin of 10 mg/KOH/g, and 5 parts of ethylene-vinyl acetate copolymer
parts by weight were dispersed in deodorized kerosene to form a 15% solution. This solution was applied by roll coating onto the aluminum foil surface of an aluminum foil laminate consisting of three layers of 12μ thick polyethylene terephthalate (PET), 7μ thick urethane adhesive, and 9μ thick aluminum foil, It was dried at 150°C for 15 seconds to form an adhesive resin layer with a thickness of 2.0 μm. This adhesive resin layer and a 50μ thick high-density polyethylene film were stacked together and passed between a steel roll and a rubber roll heated to 140°C and bonded under heat. The peel strength between the aluminum foil and the high-density polyethylene film layer of this product was extremely excellent, having the values shown in the table before and after retort sterilization (120°C for 30 minutes).

[Table] Comparative Example 1 The same operation as in Example 5 was performed using unmodified high-density polyethylene resin and unmodified polypropylene resin, but there was almost no adhesion to aluminum foil, and peel strength was measured. I couldn't do it. Comparative Example 2 Acid value 110 mgKOH/g modified with maleic anhydride
When the same operation as in Example 5 was performed using a modified high-density polyethylene resin of The strength was only about 100 to 200 g/15 mm width, and the adhesion between the aluminum foil and the high-density polyethylene film was so poor that it was not possible to measure the strength after retort sterilization. Comparative Example 3 A laminate was obtained in the same manner as in Example 1 except that the drying temperature of the coated aluminum foil was changed to 200°C. The peel strength (T peel) between the aluminum foil and the polypropylene resin layer of the obtained laminate was 500
g/15mm width, and retort sterilization treatment (120
C. for 30 minutes), the peel strength was only 550 g/15 mm width. Comparative Example 4 Using the coated aluminum foil obtained in Comparative Example 3,
A laminate was obtained in the same manner as in Example 2. The peel strength between the aluminum foil and the blend film of the obtained laminate was 400 g/15 mm width. Furthermore, the peel strength after retort sterilization was only 450 g/15 mm width. Comparative Example 5 A laminate was obtained in the same manner as in Example 5 except that a deodorized kerosene dispersion of maleic anhydride-modified polyethylene with an acid value of 0.1 mgKOH/g was used and the drying temperature was 200°C. The peel strength between the aluminum foil and high-density polyethylene film of the obtained laminate is
It was 400g/15mm wide. A peeling phenomenon occurred between the aluminum foil and the high-density polyethylene film during retort sterilization.

[Brief explanation of drawings]

FIGS. 1 and 2 are schematic process diagrams for illustrating the lamination process of the present invention. DESCRIPTION OF SYMBOLS 1... Aluminum foil or sheet, 2... Dispersion of modified polyolefin resin, 3... Heat drying oven, 4... Extruder, 5... Winding roll, 6...
...Polyolef in film, 7...Heating roll,
8...Rubber roll.

Claims (1)

[Scope of Claims] 1. An organic solvent dispersion or an aqueous dispersion of a modified polyolefin resin is applied to an aluminum foil or sheet, heated and dried to form an adhesive layer with a thickness of 0.1 to 10 μm, and then a polypropylene resin layer is formed. , a method for producing a laminate comprising thermally adhering a polyethylene resin layer or a blend layer of the two, wherein the modified polyolefin resin is a modified polypropylene resin 3 modified with an unsaturated carboxylic acid or an acid anhydride thereof. ~97 parts by weight and 97 to 3 parts by weight of a modified polyethylene resin modified with an unsaturated carboxylic acid or its acid anhydride, and dried at a drying temperature of 140°C.
A method for producing a laminate capable of retort sterilization, characterized by heating and drying at ~180°C. 2. The modified polyolefin resin contains one or more selected from the group of polyethylene and its derivatives, and polypropylene and its derivatives in an amount of 30% by weight or less based on the total weight of the modified polyolefin resin composition. A method for manufacturing a laminate according to claim 1, which is a method for producing a laminate according to claim 1. 3 The polypropylene resin layer, polyethylene resin layer, or blend layer of these two to be thermally bonded is
A method for producing a laminate according to claim 1, which is a layer obtained by melt extrusion. 4 A polypropylene resin layer, a polyethylene resin layer, or a blend layer of these two to be thermally bonded,
A method for producing a laminate according to claim 1, wherein each laminate is a preformed film. 5 A polypropylene resin layer, a polyethylene resin layer, or a blend layer of these two to be thermally bonded,
Modified polypropylene modified with an unsaturated carboxylic acid or its acid anhydride, modified polyethylene or a blend of these two, polypropylene,
A method for producing a laminate according to claim 1, which is a layer obtained by melt two-layer extrusion with polyethylene or a blend of the two. 6 The polypropylene resin layer, polyethylene resin layer, or blend layer thereof to be thermally bonded is made of modified polypropylene modified with an unsaturated carboxylic acid or its acid anhydride, modified polyethylene, or a blend of the two, and polypropylene, polyethylene, or a blend thereof. A method for producing a laminate according to claim 1, which is a film preformed by two-layer coextrusion comprising a blend of the two materials.