JPS6412318B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a solvent-free polyurethane adhesive for dry lamination. Conventionally, as packaging materials, various plastic films, metal foils, cellophane, paper, etc. are laminated together using adhesives, and laminates that take advantage of the characteristics of each film and foil are increasingly used. Known lamination methods include dry lamination, wet lamination, hot melt lamination, and extrusion lamination, but dry lamination is used for food packaging that requires high quality. The method is widely used. Traditionally, vinyl, acrylic, polyamide, epoxy, rubber, and urethane adhesives have been known as adhesives for dry lamination, but in reality, there are different types of adhesives due to adhesive strength and other processing suitability. Mostly urethane-based solvent-based dry laminating adhesives are used. However, in recent years, dry lamination using solvent-free polyurethane adhesives has been considered from the viewpoint of resource saving and pollution prevention, and some of them have already been put into practical use. These adhesives are made by combining aromatic diisocyanates in which an isocyanate group is directly bonded to an aromatic ring, such as tolylene diisocyanate (TDI) and 4,4-diphenylmethane diisocyanate (MDI), or adducts thereof, and polyols. It is a moisture-curing adhesive whose main component is a prepolymer with terminal isocyanate groups obtained by reacting at an equivalent ratio of NCO/OH > 1.0. Although these have satisfactory performance in terms of adhesiveness, they have the fatal disadvantage of poor weather resistance and easy yellowing. Therefore, the present inventor developed an aromatic diisocyanate in which an isocyanate group is not directly bonded to an aromatic ring, which is known as a non-yellowing type diisocyanate.
Attempts have been made to obtain non-yellowing, moisture-curing polyurethane adhesives by reacting cycloaliphatic diisocyanates, aliphatic diisocyanates, or their adducts with polyols, but the resulting adhesives contain free radicals. More than 1% by weight of the above diisocyanate remained. According to Article 57, Paragraph 1 of the Industrial Safety and Health Act and its related laws and regulations, if the TDI content exceeds 1% by weight, it must be labeled.
It was thought that this should be complied with, and that the amount of remaining free diisocyanate was preferably 1% by weight or less. Therefore, the present inventor reacted an aromatic diisocyanate, a cycloaliphatic diisocyanate, an aliphatic diisocyanate in which the isocyanate group is not directly bonded to an aromatic ring, or an adduct thereof with a polyol, and then used a thin film evaporator. We investigated ways to remove the remaining free diisocyanate by methods such as using the method, and succeeded in obtaining a solvent-free polyurethane adhesive for dry lamination in which substantially no free diisocyanate remains. However, with this method, (1) the viscosity of the prepolymer is high when removing the remaining free diisocyanate, it takes a lot of time to remove it, and the prepolymer is susceptible to thermal deterioration; (2) depending on the application, Since the composition of the polyol is different, it is necessary to remove the remaining free diisocyanate for each small lot, which has disadvantages such as high cost and time consuming. In order to solve these drawbacks, the inventors
As a result of further intensive studies, the present invention is based on (1) an aromatic diisocyanate, an alicyclic diisocyanate, or an aliphatic diisocyanate in which the isocyanate group is not directly bonded to an aromatic ring; A polyol having two or more hydrogen atoms and a molecular weight of 500 or less, in an equivalent ratio of NCO/
An adduct of the above diisocyanate obtained by reacting in the presence or absence of a solvent inert to the reaction at a ratio of OH≧2, and then substantially removing the remaining free diisocyanate and optionally the solvent. , (2) a hydroxy compound having one or more active hydrogens in an equivalent ratio of 1.0<
This is a solvent-free polyurethane adhesive for dry lamination comprising a reaction product obtained by reacting in the absence of a solvent at a ratio of NCO/OH≦10. According to the present invention, since the viscosity of the adduct is low, there is no thermal deterioration when removing unreacted diisocyanate, and after the adduct is produced, the composition of the polyol to be reacted with the adduct can be adjusted according to the purpose. It can be changed in various ways, so it is low cost,
The remaining free diisocyanate can be substantially removed, and a non-yellowing, solvent-free polyurethane adhesive for dry lamination that is substantially free of free diisocyanate can be obtained. In the present invention, conventionally known aromatic diisocyanates, alicyclic diisocyanates, or aliphatic diisocyanates in which the isocyanate group is not directly bonded to an aromatic ring can be used, and examples of such diisocyanates include xylylene diisocyanates, Isocyanate (XDI), metaxylylene diisocyanate (MXDI), hexamethylene diisocyanate (HMDI), hydrogenated XDI
(H ₆ XDI), Hydrogenated MDI (H ₁₂ MDI), Hydrogenated TDI
(H ₆ TDI), dimeryl diisocyanate (DDI),
Examples include lysine diisocyanate (LDI) and isophorodiisocyanate (IPDI), and mixtures thereof can also be used. Examples of polyols having a molecular weight of 500 or less having two or more active hydrogens according to the present invention include ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butylene glycol,
1,4-butanediol, 1,5-pentanediol, neopentyl glycol, hexylene glycol, hexamethylene glycol, glycerin, trimethylolpropane, polyethylene glycol (with a molecular weight of 500 or less), polypropylene glycol (with a molecular weight of 500 or less) ), pentaerythritol, etc., and mixtures thereof can also be used. If a polyol having two or more active hydrogen atoms and a molecular weight greater than 500 is used, the content of isocyanate groups in the prepolymer having terminal isocyanate groups obtained by reaction with a diisocyanate will be low, which is not preferable. In the present invention, (1) an aromatic diisocyanate, a cycloaliphatic diisocyanate, or an aliphatic diisocyanate in which the isocyanate group is not directly bonded to an aromatic ring, and a polyol having a molecular weight of 500 or less having two or more water or active hydrogen, in equivalent ratio
The reaction is carried out in the absence of a solvent at a ratio of NCO/OH≧2 to obtain a prepolymer having an isocyanate group at the end, and the free diisocyanate remaining in the obtained prepolymer and a solvent inert to the reaction are removed. The diisocyanate adduct is substantially removed by a commonly used removal method, such as a method using a thin film evaporator, to obtain the above diisocyanate adduct. The reaction between the above diisocyanate compound and water or a polyol with a molecular weight of 500 or less having two or more active hydrogen atoms is preferably carried out in the absence of a solvent, but it is preferable to carry out the reaction with an inert solvent such as toluene, xylene, methyl ethyl ketone, dioxane, etc. It may be carried out in the presence of a solvent. These solvents are preferably selected to have a relatively low boiling point so that they can be removed together with the free diisocyanate. The reaction conditions are 30 to 120°C for 30 minutes to several hours, and the hydroxyl group and isocyanate group are fully reacted.
Avoid conditions at high temperatures and for long periods of time that would cause reactions between isocyanate groups. In the present invention, "substantially removing remaining free diisocyanate" means removing isocyanate at the end so that the amount of free diisocyanate remaining in the polyurethane adhesive for dry lamination is 1% by weight or less. It is meant to remove any free diisocyanate remaining in the prepolymer containing the groups. In the present invention, the hydroxy compound having one or more active hydrogens preferably has a boiling point of 100°C or higher from the viewpoint of reaction efficiency, and such hydroxy compounds include n-amyl alcohol, isoamyl alcohol, , monohydroxy compounds like hexyl alcohol, peptyl alcohol, octyl alcohol, caprylic alcohol, nonyl alcohol, decyl alcohol, undecyl alcohol, lauryl alcohol, stearyl alcohol, ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene Glycol, propylene glycol, polypropylene glycol, polyoxypropylene glycol, 1,
3-propanediol, 1,3-butylene glycol, 1,4-butanediol, dibutylene glycol, 1,5-pentanediol, neopentyl glycol, hexylene glycol, hexamethylene glycol, 1,3-hexanediol,
glycerin, 1,2,6-hexanetriol,
These include hydroxy compounds such as trimethylolpropane, polyether polyols, polyester polyols, and mixtures thereof. The thus obtained adduct of an aromatic diisocyanate, an alicyclic diisocyanate, or an aliphatic diisocyanate in which the isocyanate group is not directly bonded to an aromatic ring, and a hydroxy compound having one or more active hydrogens. , an equivalent ratio of 1.0<NCO/OH≦10, preferably 1.1
The reaction is carried out in the absence of a solvent at a ratio of ≦NCO/OH≦10 to obtain a solvent-free polyurethane adhesive for dry lamination in which the amount of the remaining free diisocyanate is 1% by weight or less. NCO／
If the proportion of OH is smaller than the above ratio, there will be no isocyanate groups and the ability to crosslink and cure will be lost, and in the opposite case, moisture curability will similarly be poor. Moreover, when NCO/OH is 1.0 to 1.1, gelation tends to occur. The above reaction is carried out at a temperature and for a time sufficient to allow the hydroxyl group and the isocyanate group to react, and it is preferable to avoid a reaction at a high temperature and for a long time that would cause the isocyanate groups to react with each other. Further, the above reaction needs to be carried out in the absence of a solvent, and if carried out in the presence of a solvent, a step of removing the solvent is required to obtain a solvent-free adhesive, which is not industrially preferable. 1.0<
When the reaction is carried out at a ratio of NCO/OH<1.1, the viscosity of the resulting adhesive tends to increase. The solvent-free polyurethane adhesive for dry lamination according to the present invention may contain additives such as a catalyst for accelerating the reaction and an auxiliary agent for improving adhesiveness, if necessary. The solvent-free polyurethane adhesive for dry lamination according to the present invention is highly effective in adhering plastic films to each other, plastic films to aluminum foil, and the like. The present invention will be explained below with reference to Examples. In the examples, "part" means part by weight, and "%" means percent by weight. Production example 1 504 parts of HMDI was placed in a three-necked flask and kept at 100°C with stirring under a nitrogen gas stream.
90.1 parts of 4-butanediol were added dropwise (in equivalent ratio, NCO/OH=3.0). After dripping, 100
C. for 3 hours to obtain a prepolymer having terminal isocyanate groups with an NCO% of 34%. The obtained prepolymer is charged into a thin film evaporator to remove the remaining free HMDI.
An adduct of HMDI with a content of 0.43% and NCO% of 18.5% was obtained. Production Example 2 666 parts of IPDI was placed in a three-necked flask, maintained at 100°C with stirring under a nitrogen gas stream, and polypropylene glycol (molecular weight 400) was added dropwise (NCO/OH = 3.0 in equivalent ratio). After completion of the dropwise addition, the mixture was kept at 100°C for 3 hours to obtain a prepolymer having isocyanate groups at the ends. The obtained prepolymer is charged into a thin film evaporator and the remaining free
After removing IPDI, remaining free IPDI content
An adduct of IPDI of 0.57% and NCO% of 8.5% was obtained. Example 1 900 parts of the HMDI adduct obtained in Production Example 1 was placed in a three-necked flask, kept at 80°C with stirring under a nitrogen stream, and 350 parts of polypropylene glycol (molecular weight 700) was added, followed by polypropylene glycol. (molecular weight 1000) was added dropwise (in equivalent ratio, NCO/OH=2.5). After dropping, keep at 90℃ for 5 hours to remove remaining free HMDI.
An adhesive with a content of 0.19% and NCO% of 3.5% was obtained.
Table 1 shows the results of testing adhesive strength and weather resistance using the obtained adhesive and laminating under the following lamination conditions. Laminating conditions Laminator: Solvent-free adhesive lanenator (homemade) Application amount: Approx. 1.5 g/m ² (However, Al
For Foil/CPP, approximately 3~
3.5g/m ² ) Aging conditions: held at 40°C for 2 days, then left at room temperature for 2 days. Example 2 810 parts of the HMDI adduct obtained in Production Example 1 was placed in a three-necked flask, and while stirring under a nitrogen stream, 3 parts of trimethylolpropane was added, and the temperature was gradually raised to 80%. ℃. Polypropylene glycol (molecular weight 400) while keeping at 80℃
297 parts and then 700 parts of polypropylene glycol (molecular weight 2000) were added dropwise (in equivalent ratio, NCO/OH=2.5). After dropping, heat at 90℃ for 6
Keep time, remaining free HMDI content 0.15%,
An adhesive with NCO% 2.95% was obtained. Using the obtained adhesive, lamination was performed under the same conditions as in Example 1, and the results of testing the adhesive strength and weather resistance are shown in Table 1.
Shown below. Example 3 380 parts of the HMDI adduct obtained in Production Example 1 was placed in a three-necked flask, kept at 80°C with stirring under a nitrogen stream, and treated with polyester polyol F-15-22 (manufactured by Asahi Denka). 1000 parts were added dropwise (in equivalent ratio, NCO/OH=2.5). After finishing dropping,
It was kept at 90° C. for 6 hours to obtain an adhesive with residual free HMDI content of 0.15% and NCO% of 1.95%. Using the obtained adhesive, lamination was carried out under the same conditions as in Example 1, and the adhesive strength and weather resistance were tested. Table 1 shows the results. Example 4 988 parts of the IPDI adduct obtained in Production Example 2 were charged into a three-necked flask, maintained at 100°C with stirring under a nitrogen stream, and 4.5 parts of 1,4-butanediol were added, followed by polypropylene. 500 parts of glycol (molecular weight 1000) was added dropwise. After dropping, keep at 100℃ for 5 hours to remove remaining free IPDI.
An adhesive with a content of 0.28% and an NCO% of 2.4% was obtained.
Using the obtained adhesive, lamination was carried out under the same conditions as in Example 1, and the adhesive strength and weather resistance were tested. Table 1 shows the results. Reference Example 858 parts of MDI was charged into a three-necked flask, kept at 80°C with stirring under a nitrogen stream, and 350 parts of polypropylene glycol (molecular weight 700) was then added.
650 parts of polypropylene glycol (molecular weight 1000) were added dropwise. After the dropping was completed, the adhesive was kept at 90°C for 7 hours to obtain an adhesive with an NCO% of 2.40%. Using the obtained adhesive, lamination was carried out under the same conditions as in Example 1, and the adhesive strength and weather resistance were tested. Table 1 shows the results.

[Table] In Table 1, Adhesive strength: No ND data Heat seal strength: FF film breakage, No ND data Weather resistance: No change, x Yellowing. respectively. The conditions for the above test are as follows. (1) Test conditions for adhesion and heat-sealing strength Sample width: 15mm Peeling angle: 90° (T-shaped peeling) Peeling speed: 30cm/min Measurement atmosphere: 20℃, 65%RH (2) Heat-sealing conditions LDPE used Time: 160℃, 2Kg/cm ² , seal in 1 second When using HDPE or CPP: 180℃, 2Kg/cm ² ,
Seal in 1 second (3) Film and aluminum foil used PET: Polyethylene terephthalate film “Lumirror” manufactured by Toray Industries, Inc. (thickness 12 μm) NY: Polyamide film “Emblem” manufactured by Unitika Co., Ltd. (thickness 15 μm) LDPE : Low-density polyethylene film "TTB" manufactured by Tamapoly Co., Ltd. (thickness 60μm) HDPE: High-density polyethylene film "NB-1" manufactured by Tamapoly Co., Ltd. (thickness 60μm) CPP: Non-stretched manufactured by Toray Industries, Inc. Polypropylene film #3701 (thickness 70μm) Aluminum foil: Showa Aluminum Co., Ltd. aluminum foil (thickness 9μm) (4) Weather resistance test conditions Fade meter used. Results after 72 hours. As can be seen from Table 1, the adhesive properties of the polyurethane adhesive for dry lamination of the present invention are equivalent to those of conventional polyurethane adhesives for dry lamination obtained from a polyol and an aromatic diisocyanate in which an isocyanate group is directly bonded to an aromatic ring. However, it has much better weather resistance.

Claims (1)

[Claims] 1 (1) An aromatic diisocyanate, a cycloaliphatic diisocyanate, or an aliphatic diisocyanate in which the isocyanate group is not directly bonded to an aromatic ring, and a polyol with a molecular weight of 500 or less having two or more of water or active hydrogen in an equivalent ratio of NCO An adduct of the above diisocyanate obtained by reacting in the presence or absence of a solvent inert to the reaction at a ratio of /CH≧2, and then substantially removing the remaining free diisocyanate and optionally the solvent. and,
(2) It is characterized by using a reaction product obtained by reacting a hydroxy compound having one or more active hydrogens at an equivalent ratio of 1.0<NCO/OH≦10 in the absence of a solvent. A solvent-free polyurethane adhesive for dry lamination.