JPH0324509B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improved heat-sensitive ethylene copolymer film adhesive that has a well-balanced combination of low-temperature melt adhesion and heat-resistant adhesion, and more specifically to a copolymer of ethylene and α,β-unsaturated carboxylic acid. In this step, a polyamide oligomer is introduced into the side chain of the ionomer by catalytically reacting the polyamide oligomer with an ethylene copolymer (hereinafter referred to as an ionomer) in which a portion of the acid in the copolymer has been neutralized with metal ions. The present invention relates to a film adhesive made of. In general, the properties required for resins for heat-sensitive film adhesives include economical film formability, as well as lower temperature in terms of adhesive work efficiency and damage caused by heat deformation and deterioration during bonding of base materials. There has been a strong demand for properties that allow for melt bonding (low-temperature adhesion) and at the same time maintain adhesive strength during thermal bonding and when the bonded structure is exposed to high temperatures (heat-resistant adhesion). However, these properties are contradictory, and it has been difficult to obtain a resin film that has a well-balanced combination of properties such as film formability, low-temperature adhesion, and heat-resistant adhesion. For example, polyolefin resins, especially ethylene copolymers, such as ethylene-vinyl acetate copolymers, ethylene-vinyl acetate copolymers, etc.
Film adhesives such as acrylic acid ester copolymers and ionomers can be bonded at relatively low temperatures of around 100°C and have excellent low-temperature adhesion properties, but these copolymer films have relatively low melting points; Since the melt viscosity is lower than that, the heat-resistant adhesive property is poor. On the other hand, resin films with high melting points such as polyamide and polyester resins are known as heat-resistant films, but their melt viscosity has a large temperature dependence above the melting point, and the melt viscosity rapidly decreases, resulting in There is a problem in maintaining adhesive strength, and the strength of the molten film is low, making it difficult to form a film by the inflation method, making it economically poor. Furthermore, polyester-based adhesives have poor low-temperature adhesion. The present inventors have achieved economically advantageous film formability,
While taking advantage of the properties of ethylene copolymer-based heat-sensitive film adhesives such as low-temperature adhesion, we have improved the heat-resistant adhesion, which is a drawback of these adhesives, and have achieved the various properties required for heat-sensitive film adhesives. As a result of intensive studies to obtain a heat-sensitive film adhesive with a well-balanced combination, we identified an ionomer, that is, an ethylene-α,β-unsaturated carboxylic acid copolymer, which was 5 to 50% ionized with zinc ions, and added lactam or A polyamide oligomer derived from ω-aminocarboxylic acid, one end is a primary amino group and the other end has 1 to 20 carbon atoms.
3 to 3 of polyamide oligomers having an average degree of polymerization of 4 to 35 terminated with N-alkylamide groups of
It was discovered that a graft modified product obtained by catalytically reacting less than 20% by weight can achieve the above object, leading to the completion of the present invention. That is, the present invention relates to an ethylene copolymer-based heat-sensitive film adhesive having a well-balanced combination of economical film formability, low-temperature adhesion, and heat-resistant adhesion. In the present invention, the low-temperature adhesion and heat-resistant adhesion refer to the heat-sealing temperature and shear bond failure temperature, which will be described later, respectively. Among ethylene copolymers, ionomers have the advantages of low-temperature adhesion, adhesion to base materials such as wood and metal, film strength, film formability, and ease of handling because the film does not block easily. Since the melting point is relatively low, if the adhesive part is exposed to high temperatures above the melting point, the adhesive strength cannot be maintained, and it cannot be used for adhesive applications that are used at high temperatures. It is known that the heat resistance of the ionomer can be improved by grafting a polyamide oligomer onto the ionomer, as measured by a thermal deformation test. (Japanese Patent Publication No. 55-21489). However, the modified ionomers obtained by these methods contain 20% of the ionomer in order to improve heat resistance.
By adding or grafting more than % by weight of polyamide or polyamide oligomer, it shows a certain improvement effect as a heat-resistant hot melt adhesive. There are problems such as being exposed. In addition, no further improvement in heat-resistant adhesion is observed at 20% by weight or more. Furthermore, in order to mold the modified ionomer into a film, it is necessary to mold it at a temperature higher than the melting point of the polyamide or polyamide oligomer in the modified ionomer.
Since the melt viscosity of the resin is extremely low and the molten resin film is not stable during film molding, film molding by the inflation method is difficult and uneconomical. Needless to say, these drawbacks become more noticeable as the amount of polyamide or polyamide oligomer added increases. This is a serious drawback for film adhesives. Examples of the ethylene-α,β-unsaturated carboxylic acids that are the base resin of the ionomer used in the present invention include ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-itaconic acid copolymer, and ethylene-acrylic acid. Examples include -methyl methacrylate copolymer, ethylene-methacrylic acid-ethyl acrylate copolymer, and ethylene-methacrylic acid-vinyl acetate copolymer. Further, if necessary, a blend of these copolymers with other thermoplastic resins can also be used. The graft modified product in the present invention can be produced by catalytically kneading the ionomer and polyamide oligomer at a temperature above the melting point of the base ionomer, preferably 150 to 250°C. The reactor may be of any type as long as it melts and kneads the polymer, but a screw extruder is suitable. In this case, the ionomer is ionized with zinc ions from the viewpoint of reactivity with the polyamide oligomer, and the degree of ionization is 5 to 50% from the viewpoint of improving heat-resistant adhesion and reactivity by graft modification of the polyamide oligomer. Yes, preferably 10-40%
It is. Ionomers ionized with metals other than zinc, such as sodium, potassium, magnesium, etc., do not have the effect of promoting the reaction when the carboxylic acid in the ionomer and the amino group end of the polyamide oligomer react and bond, so ionization with these metals does not have the effect of promoting the reaction. ionomers are not suitable. Furthermore, if the degree of ionization is less than 5%, the reaction promotion effect of zinc ions will be lost, and the degree of ionization will be 50%.
Above that amount, no remarkable heat-resistant adhesion improvement effect is exhibited. In general, the higher the degree of ionization of an ionomer, the better the heat-resistant adhesion. However, when graft-modifying an ionomer with a polyamide oligomer, an ionomer with the above degree of ionization is more effective in improving heat-resistant adhesion than an ionomer with a high degree of ionization. Gives greater and higher heat resistant adhesion. This is because the mechanism by which heat-resistant adhesion is improved is that the polyamide chain with a high melting point is bonded to the main chain of the ionomer, and that the intermolecular and molecular It is presumed that this is because the viscosity of the graft modified product becomes extremely high in a temperature range above the melting point of the ionomer and below the melting point of the polyamide oligomer and under low shear stress due to the synergistic effect of internal interactions. This estimation is based on ethylene-α, β, where the grafting reaction is difficult to proceed.
This is supported by the fact that a blend of an unsaturated carboxylic acid copolymer and a polyamide oligomer or a simple blend of an ionomer and a high molecular weight polyamide hardly improves heat-resistant adhesive properties.
This has not been known from conventionally known techniques. In the present invention, it is particularly important that the amount of polyamide oligomer in the graft modified product is from 3 to less than 20% by weight in order to complete the present invention. In other words, if the amount of grafted polyamide oligomer exceeds 20% by weight, not only will the advantages of ionomer's adhesive properties and low-temperature adhesive properties be greatly impaired, but also
Since the melt strength of the resin is low and the molten film is not stable, inflation molding is impossible and it is economically unsuitable as a film adhesive. The polyamide oligomer used in the present invention has one end terminated with a primary amine group and the other end terminated with an N-alkylamide group having 1 to 20 carbon atoms. This is to prevent further polymerization of the oligomer due to the temperature during the graft reaction.
The polyamide oligomer uses lactam or ω-aminocarboxylic acid as a monomer and n-alkylamine as an end capping agent. The most preferred polyamide oligomers include polycaprolactam, polylaurolactam, and copolymerized polylactams. The preferred average degree of polymerization of the oligomer is 4 to 35; if the average degree of polymerization is less than 4, the effect of improving heat-resistant adhesion is small, and if it is greater than 35, the grafting reaction rate becomes slow, making it impractical. The heat-sensitive film adhesive obtained by the present invention retains the advantages of ionomers, such as low-temperature adhesion and film processability, and is made of polyamide and polyester, which have been conventionally used as heat-resistant film adhesives. It exhibits heat-resistant adhesion properties that surpass those of conventional heat-sensitive film adhesives. The advantage of the properties of these film adhesives is that they can not only withstand use at high temperatures, but also allow the bonded structure to be moved or to apply stress to the bonded area while the bonded area is at a high temperature after thermal bonding. Therefore, when bonding materials with low thermal conductivity such as wood or asbestos, there is no need for cooling time in the bonding cycle, which is convenient for improving work efficiency. The heat-sensitive film adhesive of the present invention can be applied to metals, paper,
It adheres well to wood, glass, asbestos, various resins, etc., and is useful for building materials, woodworking, automobile parts, electrical products, aircraft parts, etc. The present invention will be specifically explained below with reference to Examples, but the present invention is not limited thereto in any way. The physical property values shown in each example were measured by the following method. (Measurement method) (1) Shear bond failure temperature (measured as an index of heat-resistant adhesion) Two soft aluminum plates are glued together with film adhesive (bonding temperature 200℃, bonding area 1.5cm ² ), and one aluminum plate is is suspended in an oven with a vertical load applied to it. Heat the oven to 50℃ at a heating rate of 15℃/hr.
Measure the temperature at which the adhesive part breaks down. Two types of loads were used: 100 g/1.5 cm ² and 500 g/1.5 cm ² . (2) Heat-sealability (measured as an index of low-temperature adhesion) Two adhesive films are sandwiched between seal bars and heat-bonded using pressure. Determine the minimum temperature at which thermal bonding is possible by measuring bonding temperature and seal strength. The heat sealing conditions were a pressure of 2 kg/cm ² , a sealing time of 0.7 seconds, a sealing width of 5 mm, and one side heating, and the sealing strength was determined by a 90° peel test. The contents of the ionomers used in the examples are as follows.

[Table] * Isobutyl acrylate Example 1 Ionomer-1 pellets and polyamide oligomer (polycaprolactam, number average degree of polymerization
Table 2.
After dry blending at the ratio shown in Figure 1, the mixture was fed to a single screw extruder (screw diameter 30 mm, L/D = 32) and kneaded and extruded to obtain pellets of a graft copolymer of polyamide oligomer and ionomer. The resin temperature in the extruder is approximately 220℃, the die temperature is approximately 200℃, the screw rotation speed is 45 revolutions per minute, and the average residence time of the resin in the extruder is approximately 3 minutes.
It was hot in 30 seconds. The resulting pellets were transparent. This pellet was processed into an inflation film using an extruder with a screw diameter of 30 mm. The resin temperature during film molding was 200 to 220°C, and the film thickness was 100 μm. Film molding was easy and there were no problems such as valve meltdown, film deformation, or blocking. The obtained film was transparent. The heat-resistant adhesive properties of these films were measured by shear bond failure temperature, and the heat-resistant adhesive properties were significantly improved compared to the original ionomer. The results are shown in Table 2. Comparative Example 1. Reference Example 1 Table 2 shows the shear bond failure temperatures of the ionomer film of Example 1, polyamide and polyester for thermal bonding as a comparative example and a reference example regarding the heat-resistant adhesive properties of the film.

[Table] Example 2 Comparative Example 2 The polyamide oligomer used in Example 1 was added to ionomer 2 in accordance with the method of Example 1, respectively.
10, 15% by weight grafted. This graft copolymer was processed into a film in the same manner as in Example 1. Film processing was easy and a transparent film was obtained. As a comparative example, 5, 10, and 15% by weight of high molecular weight polyamide (Amiran CM-1021, manufactured by Toray Industries, Inc., nylon 6, melting point 215°C) were blended with the same ionomer using an extruder according to the method of Example 1. . This blended resin was processed into a film in the same manner as in Example 1. Although the film processing was easy, a translucent film was obtained. Next, we measured the heat-resistant adhesion of the film of the ionomer grafted with this polyamide oligomer and the ionomer blended with nylon 6 by shear bond failure temperature, and found that the heat-resistant adhesion of the polyamide oligomer-grafted ionomer was significantly improved. On the other hand, with the ionomer blended with nylon 6, almost no improvement in heat-resistant adhesion was observed. The results are shown in Table 3.

[Table] Example 3 Comparative Example 3 In the same manner as in Example 1, the polyamide oligomer used in Example 1 was grafted onto the ionomer shown in Table 4. As the amount of grafted polyamide oligomer was increased, when the amount of grafted oligomer exceeded 20% by weight, the resulting graft copolymer became opaque, and the resin pressure in the extruder decreased rapidly, causing the resin to come out of the extruder. A phenomenon in which the strands hung down from the die in the form of threads appeared. When the obtained graft copolymer was formed into a film in the same manner as in Example 1, it was found that in the graft copolymer in which the oligomer graft amount exceeded 20% by weight, bubble meltdown occurred and film formation could not be performed. . In addition, when we measured the adhesive strength of this graft copolymer to an aluminum plate, we found that those with an oligomer graft amount exceeding 20% by weight had significantly lower adhesive strength than those with a lower graft amount, and were therefore unsuitable as adhesives. It turns out that it is.

[Table] Comparative Example 4 Using the same equipment and under the same conditions as Example 1, an ionomer with a high degree of ionization, an ionomer whose metal ion species is not zinc, and the polyamide oligomer used in Example 1 were used as the ethylene/methacrylic acid copolymer. An attempt was made to graft 10% by weight. Although it is unclear whether or not a graft reaction occurred, the product was milky white and opaque or translucent. The product was processed into a 100 μm thick film in the same manner as in Example 1. Although the films were easy to process, they were translucent. When the heat-resistant adhesive properties and adhesive strength with aluminum were measured for this film, it was found that the degree of improvement in heat-resistant adhesive properties was very small compared to Example 1, or the adhesive strength was insufficient. It was insufficient as a drug. The results are shown in Table 5.

[Table] Example 4 Comparative Example 5 Regarding the films of polyamide graft ionomer, ionomer, polyamide, and polyester shown in Table 6, the low temperature adhesion, heat resistant adhesion, and adhesive strength were measured in terms of heat seal strength, shear bond failure temperature, aluminum, respectively. It was measured by the adhesive force with the board. The polyamide oligomers of Examples had low-temperature adhesion and adhesive strength at the same level and significantly superior heat-resistant adhesion compared to conventional heat-sensitive film adhesives. On the other hand, the polyamide oligomer graft ionomer (Comparative Example 5) with a high polyamide oligomer content of 25% by weight has good heat-resistant adhesion, but
The heat-sealability and adhesive strength were insufficient, and the adhesive was unsatisfactory as a heat-sensitive film adhesive.

【table】

[Table] Example 5 Reference Example The adhesion between the polyamide oligomer graft ionomer film shown in Table 7 and various substrates was measured by shear adhesive strength. Similar measurements were also made for the commercially available heat-sensitive film adhesives shown in Table 6 for comparison. All had adhesive strength sufficient for practical use. In addition, when bonding with polyamide oligomer graft ionomer, it was possible to remove the bonded object without cooling it after bonding, but with commercially available adhesives, if you move the bonded object without cooling it, the bonded part will move and break. It was taken out after cooling. The results are shown in Table 7.

【table】

[Table] Example 6 Comparative Example 6 Polyamide oligomers (polycaprolactam, terminal carboxyl group blocked with n-hexylamine) having different degrees of polymerization shown in Table 8 were added to ionomer 1.
A mixture of 90% by weight of ionomer and 10% by weight of polyamide oligomer was mixed and reacted using a Brabender Plastograph at 220° C. for 10 minutes. The reaction product was molded into a 200 μm thick film by hot pressing, and heat-resistant adhesiveness was measured by shearing adhesive failure temperature. Those with a low average degree of polymerization of the oligomer had a poor degree of improvement in heat-resistant adhesion in practical terms, and those with a high degree of oligomerization had insufficient grafting reaction, resulting in a milky white film and little improvement in heat-resistant adhesion. The average degree of polymerization of the oligomer used was suitably about 4 to 35.

【table】

Claims (1)

[Claims] 1 Polyamide derived from lactam or ω-aminocarboxylic acid with more than 80% by weight and 97% by weight or less of a basic ionomer made of ethylene/α,β-unsaturated carboxylic acid copolymer ionized with 5 to 50% zinc ions 3% by weight or more of a polyamide oligomer having an average degree of polymerization of 4 to 35, which is an oligomer and has a primary amino group at one end and an N-alkylamide group having 1 to 20 carbon atoms at the other end; A heat-sensitive film adhesive made by grafting less than % by weight into side chains.