JPS6115111B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a hot melt adhesive containing linear polyester as a main ingredient. For more details
0.65 mol or more of 1,4-butanediol containing 20 mol% or more of 0 mol% or more of 1,6 hexanediol as a diol component for 1 mol of dibasic acid component of which 85 mol% or more and 100 mol% or less is terephthalic acid. The present invention relates to a hot melt adhesive based on a polyester containing 0.97 mol and polyethylene glycol having a molecular weight of 150 to 550 in a proportion of 0.03 mol to 0.35 mol. By using the polyester composition of the present invention, it is possible to obtain an adhesive that exhibits strong adhesive strength and has excellent heat resistance and water resistance. Linear polyesters have been widely used as fibers, films, elastomers, etc., but aromatic polyesters are unsuitable for adhesive applications due to their rigid molecules and crystallinity. In the case of aliphatic polyester, on the other hand, it has the disadvantages of being too flexible and having a low melting point, so it has not yet achieved an important position. Hot melt adhesives have been recognized for their pollution-free and energy-saving features.
Its usage has been increasing in recent years. Hot melt adhesives utilize the process of heat melting and cooling solidification of adhesives without using water or organic solvents, so they should be particularly effective in bonding impermeable materials, especially metals and plastics. be. Polyester basically consists of a dibasic acid and a diol, but it can have various physical properties depending on the selection of its constituent components. In particular, in the field of synthetic fibers, which developed industrially from an early stage, there have been many reports and proposals in academic literature, patents, etc. about how important physical properties of fibers change depending on the selection of constituent components. However, there are very few reports or proposals regarding the composition of polyester suitable for hot melt adhesives, particularly for metal bonding. Although it is possible to select the constituent components of polyester in order to improve one specific physical property, doing so also alters other physical properties, often resulting in a worsening of the property. . It is very difficult to improve certain physical properties while maintaining them at appropriate levels. From this point of view, the present inventors determined various physical properties and arrived at the composition of the present invention. It is conventionally known to copolymerize polyethylene terephthalate with polyethylene glycol.
According to D.Coleman (J.Polym.Sci., 14, 15 (1954)), when polyethylene glycol with a molecular weight of 600 to 2800 is copolymerized with polyethylene terephthalate, the melting point and secondary transition point decrease, but the dyeability improves. .
Also, according to Nittoku Koko No. 16146, the molecular weight is 800~
It has been shown that 2500 polyoxytetramethylene glycol is copolymerized with polyethylene terephthalate and then applied to a fabric to be used as a heat-fusible adhesive fabric. The tensile shear adhesive strength when hot-melt bonding of stainless steel with this type of polyester is several tens of kg/cm ² , and the tensile shear adhesive strength when similarly bonded with polyethylene terephthalate film is several tens to 100 kg/cm ² at most. It is. That is, it seemed that the adhesive strength of polyethylene terephthalate could not be increased even if polyoxyalkylene glycol was copolymerized. Furthermore, for adhesion between metals, it is practically desired to have a tensile shear adhesive strength of 150 to 500 Kg/cm ² or more, which is assumed to be the structural adhesive strength, but the above value does not satisfy this. Even if the methylene chain length of the diol component is sequentially extended to poly(trimethylene terephthalate), poly(tetramethylene terephthalate), poly(pentamethylene terephthalate), and poly(hexamethylene terephthalate), the tensile shear adhesive strength is 60 to 110 Kg/ ^cm2 , and further improvement is desired. However, when using the adhesive composition according to the present invention, not only a tensile shear adhesive strength of around 200 kg/cm ² is achieved, but also, as is already well known in adhesives, those with high tensile shear adhesive strength have a high peel adhesive strength. Good peel adhesion strength is also achieved without following the general rule that it is low. In the adhesive composition of the present invention, the dibasic acid component of the linear polyester as the main ingredient is terephthalic acid or terephthalic acid in which 15 mol% or less of terephthalic acid has been replaced with another copolymerizable dibasic acid. Isophthalic acid, 1,
2-bis(p-carboxyphenoxy)ethane,
These are aromatic dicarboxylic acids such as 2,2-bis(p-carboxyphenyl)propane, and aliphatic dicarboxylic acids such as succinic acid, adipic acid, and sebacic acid. These copolymerizable dibasic acid components are employed within a range that does not significantly inhibit the melting point and crystallinity of the polyester, and can be used when it is desired to improve peel strength even at the expense of a slight decrease in tensile shear adhesive strength. From this point of view, the amount of copolymerization is preferably 0 or 15 mol % or less of the dibasic acid component, but preferably 0 or 10 mol % or less. Due to excessive co-weight, the tensile shear bond strength decreases significantly;
Peel strength no longer improves, and the solidification rate of the molten polymer decreases when it cools, making short-term, high-speed bonding, one of the advantages of hot-melt adhesives, difficult, and the heat and water resistance of the adhesive decreases significantly. It is inappropriate to do so. Although digalponic acid has been mentioned above as a dibasic acid component of polyester, its lower alkyl ester is equally used in actual polyester production. One of the diol components of the polyester in the present invention is 1,4-butanediol containing 0 and 20 mol% or less of 1,6-hexanediol, and the other is polyethylene glycol having a molecular weight of 150 to 400. 1,4-butanediol is essential as the first diol component. 1,
Good adhesion cannot be obtained unless 4-butanediol is used. In the case of other types of polyethylene glycol, due to the high melting point of polyester, there is a lack of adhesive strength that may be due to various causes such as decomposition due to the heat of the polymer during melt bonding.
Furthermore, since polyester has a low melting point, it lacks heat resistance and is therefore unsuitable as an adhesive, so 1,4-butanediol is most suitable. Furthermore, high-speed adhesion is possible by using 1,4-butanediol as an essential component of the diol, which is thought to be due to the high crystallization rate of terephthalate polyester from 1,4-butanediol. As in the case of the dibasic acid component mentioned above, 1,
It is possible to replace a part of 4-butanediol with 1,6-hexanediol, and the amount is zero or more.
It is 20 mol% or less. In particular, it is preferably 0 or more and 15 mol% or less. Another essential component of the diol component of the polyester in the present invention is polyethylene glycol having a molecular weight of 150 to 400. Although polyethylene glycols of various molecular weights can be copolymerized,
A high degree of adhesive strength can be obtained only if the molecular weight is selected within this range, and if the amount is copolymerized as described below. It is only when polyethylene glycol in this molecular weight range is selected as a constituent of the polyester composition described above from terephthalic acid and 1,4-butanediol that the possibility of obtaining a high degree of adhesive strength is realized. Moreover, in this case, it is surprising that both the tensile shear adhesive strength and the peel adhesive strength, both of which are important in practical terms, have high values. If the molecular weight is outside the above range, the adhesive strength will be low and unsuitable, and the above range is preferable. In particular, 150 or more and 300 or less are preferable. A molecular weight of 150 corresponds to triethylene glycol. As the molecular weight increases, it becomes difficult to obtain a polyethylene glycol consisting of a single component in terms of molecular weight, but in that case a mixture of polyethylene glycols, substantially all of which have a molecular weight within the above range, is used. Although polypropylene glycol and polytetramethyl glycol, which are analogs of polyethylene glycol, can be copolymerized, the adhesive strength of the resulting polyester is unsuitable. The diol component in the polyester in the present invention has a molecular weight of 150 to 400 per mole of the dibasic acid component.
0.03 mol or more of the following polyethylene glycols
The 1,4-butanediol component containing 0 to 20 mol% of 1,6-hexanediol is 0.72 to 0.97 mol. If the amount of polyethylene glycol component is small, the adhesive strength, especially the peel adhesive strength, will be low, and even if the amount is appropriately large, the adhesive strength will be low, and the solidification rate of the eluted polyester will be slow when cooling, making it unsuitable for high-speed bonding. Sexuality also becomes inferior. The polyethylene glycol component is preferably 0.05 or more and 0.2 mole or less. The polyester having the composition described above solidifies within a very short time upon cooling after elution, and has excellent heat resistance and
This realizes strong adhesion with excellent water resistance.
The melting point of polyester differs depending on the monomer composition, but the above-mentioned polyester generally has a melting point of 160
Exists in the range of ℃ or higher and 210℃ or lower. The polyester in the present invention may contain trace amounts of catalysts and stabilizers used during its polymerization. Examples of these are Ti, Zr, Zn, Ca, Mg, Sb, Sn,
Examples include compounds of elements such as P. The degree of polymerization of polyester is important, and in a mixed solvent of phenol and tetrachloroethane (weight ratio 1:1),
A high viscosity material with an intrinsic viscosity of about 0.5 or more at 30°C, particularly 0.6 or more is desirable. In order to facilitate its use as a hot-melt adhesive, the polyester in the present invention contains antioxidants, particularly 2,6-di-tert-butyl-para-cresol and 2,2-methylene-bis(4-methyl-6-tert). - Phenolic antioxidants such as butylphenol), substances to impart conductivity such as metal or carbon powders, metal oxides to enable dielectric heating melting such as iron oxide, and titanium oxide as a coloring agent. It is possible to appropriately select and mix various pigments such as , and various polymers such as polyolefin, polyamide, polycarbonate, etc. for the purpose of adjusting melt viscosity or increasing the amount, depending on the purpose of adhesion. The adhesive composition thus obtained is molded into films, plates, fibers, strings, chips, powders, etc. by melt molding. Alternatively, it is possible to dissolve the material in a solvent and then evaporate the solvent or add a non-solvent to precipitate it into a shape, but this is more complicated than the melting method. Substances that can be bonded with the adhesive of the present invention include metals, plastics, fibers, films, wood, paper, etc., and it exhibits particularly excellent adhesion effects between metals. The metal surface may be coated with a conventionally known primer. For example, when bonding metal surfaces together, the metal surfaces may be coated with phenolic resin and then the phenolic resin surfaces may be bonded together using the adhesive of the present invention. The adhesive of the present invention is sandwiched in a solid state between adherends, and the entire body is hot-pressed. Once the adhesive has melted, the adherends are cooled while maintaining the predetermined bonding position, and the adhesive is solidified. Either apply the adhesive melt to the bonding site of one of the adherends in advance, join it with the other adherend, and then cool and bond, or cool and solidify the melt once and then combine it with the other adherend. The adhesive can be bonded by hot-pressing the whole, melting the adhesive again and cooling it, or by applying adhesive to the other side of the adherend in advance and bonding in a similar manner. Ru. The temperature for melting the adhesive is several degrees or more than the melting point of polyester.
A temperature range of 50°C higher, particularly a temperature range of 10 to 40°C higher, is suitable. Pressure is 0.5 to 30Kg/cm ² , especially 2 to 20Kg/
A range of cm ² is appropriate. The heat-pressing time is sufficient as long as the time required for the polyester to melt and exhibit fluidity is sufficient. The time it takes to show fluidity varies depending on the shape and size of the adherend, so it cannot be uniquely determined, but it may be a very short time after it starts to show fluidity. Keeping the polyester in a molten state for an excessively long time is unsuitable because it causes thermal oxidative decomposition of the polyester. As the means for heating, melting and cooling the adhesive in the present invention, conventionally known means are applied, and no new methods are required. Examples Examples 1 to 8 and Reference Examples 1 to 15, 25 Dimethyl terephthalate, 1,4-butanediol, and polyethylene glycol were added to dimethyl terephthalate in an amount equivalent to 0.03 wt% of tetra-n-
It was charged into a glass reactor together with butyl titanate and heated to 200°C while stirring. After continuing the reaction for 90 minutes while continuously removing the generated methanol from the system, the temperature was raised to 260℃, and the temperature was increased to 0.2 to 0.6 mm.
Polymerization was carried out under reduced pressure of Hgabs. for ~2 hours to obtain polyester. After taking the polyester out of the reactor and turning it into powder, it was placed between two Teflon sheets, melted using a hot press at a temperature 20 to 30 degrees Celsius higher than the melting point of polyester, and then formed into a film using a cooling press. . The thickness of the film was approximately 120μ. On the other hand, Japanese Industrial Standard JIS-K-6848-1976,
In order to conduct adhesive strength tests in accordance with JIS-K-6850-1976 and JIS-K-6854-1973,
Prepare an adherend metal piece specified in the same standard, sandwich the film between the two metal pieces, place it between two larger holding plates, and set the entire body to a temperature 40°C higher than the melting point of polyester. It was hot pressed using a hot press. After about 30 seconds after the adhesive melted, the test piece was taken out and cooled with water to complete the adhesion. The thickness of the adhesive layer was adjusted to 100μ using a spacer. The adherend was wiped of water, air-dried in the test room for two days, and the humidity was controlled before it was subjected to adhesive strength measurement. Adhesive strength measurement: 20±5℃, 65±20%
It was conducted at RH. The results are summarized in Table 1 along with comparative reference examples. The composition analysis of polyester is
The analysis was carried out by H ¹ -NMR and gas chromatography of the ethanol decomposition product.

【table】

[Table] It is clear from Table 1 that terephthalic acid, 1,4-butanediol, and polyethylene glycol of a specific molecular weight and copolymerization amount give high adhesive strength. Examples 9 and 11 and Reference Examples 16 to 22 and 24 Polyesters were synthesized using the same method as in the above examples, but using different alkylene glycols, and an adhesion test was conducted. The results are summarized in Table 2, and it is clear from Table 2 that high adhesive strength is provided only when the constituent components of the polyester in the present invention are as described in the text.

Table: Example 12 The method of Example 2 was repeated, substituting 10 mole % of dimethyl terephthalate in Example 2 with dimethyl isophthalate. The tensile shear adhesive strength and T-peel adhesive strength of the steel plates bonded together were 164 Kg/cm ² and 5.3 Kg/25 mm, respectively. On the other hand, when dimethyl isophthalate was 20 mol %, the adhesive strengths were 78 Kg/cm ² and 5.8 Kg/25 mm, respectively. Note that the same results as above were obtained when dimethyl adipate or dimethyl sebacate was used instead of dimethyl isophthalate. Reference Example 23 The method of Reference Example 1 was repeated by replacing 10 or 20 mol% of dimethyl terephthalate with dimethyl 1,10-decanedicarboxylate.
When adhering steel plates together, the tensile shear adhesive strength is 63 or 55 Kg/cm ² and the T-peel adhesive strength is 0.1 and 0.8.
Kg/25mm. Example 13 Several adhesive test pieces from the above examples and reference examples were immersed in boiling water at 100°C for 1 hour to see how the tensile shear adhesive strength changed as a result of immersion in hot water. In the cases of Examples 2, 3, 4, and 6, there was no substantial decrease in strength, but in the cases of Reference Examples 5, 6, 8, and 9, there was a large decrease in strength, and in some cases, the strength of the test piece decreased. Adhesion failure occurred during the automatic immersion process. It should be noted that the results of hot water immersion were similar for the polyester according to the present invention described in Examples and its comparative reference examples. The effects of the adhesive of the present invention have been specifically shown above in a form in which the effects are most clearly manifested, but as already mentioned, when the specific polyester of the present invention is used as the main ingredient and other substances are mixed with it, A similar effect can be seen in

Claims (1)

[Claims] 1 As an acid component, terephthalic acid or 85 mol%
1 mole of the dibasic acid component of which the above is terephthalic acid and 1,4-butanediol or 1,4-butanediol containing 20 mol% or less of 1,6-hexanediol as the diol component, 0.72 mol or more and 0.97 mol or less, and a hot melt adhesive for metals whose main ingredient is a polyester obtained by polycondensing 0.03 mol to 0.28 mol of polyethylene glycol with a molecular weight of 150 to 400.