WO2004053012A1

WO2004053012A1 - Polyurethane-amide adhesive using glycerol and fatty acid

Info

Publication number: WO2004053012A1
Application number: PCT/KR2003/002651
Authority: WO
Inventors: Hyuck-Jung Gwon; Heon Park; Whan-Gi Kim; Eun-Chang KANG; Kyeong-Heui MIN; Byung-June AHN
Original assignee: Konkuk University
Priority date: 2002-12-09
Filing date: 2003-12-04
Publication date: 2004-06-24
Also published as: KR100540796B1; AU2003302914A1; KR20040050260A

Abstract

The present invention relates to polyurethane-amide adhesives using glycerol and fatty acid, and more particularly to adhesives produced by reacting polymethylenebisphenylisocyanate with the fatty acid and glycerol obtained from vegetable oil, edible oil or waste edible oil. According to the present invention, the adhesives for the commercially available industrial materials can be produced from the polymethylenebisphenylisocyanate (PMDI) as a raw material of urethane-based adhesives, and the fatty acid and glycerol obtainable from vegetable oils, so that these adhesives can be used as an environment-friendly thermosetting material. The inventive adhesives thus obtained are widely used as wood adhesives, industrial adhesives, or adhesives for electric/electronic materials, or for the production of urethane foams.

Description

POLYURETHANE-AMIDE ADHESIVE USING GLYCEROL AND FATTY ACID

Technical Field

The present invention relates to polyurethane-amide adhesives using glycerol and fatty acid, and more particularly to adhesives produced by reacting polymethylenebisphenylisocyanate with the fatty acid and glycerol from vegetable oil, edible oil or waste edible oil.

Background Art

In Korea, with an increasing interest in new materials, the development of the new materials is being performed in research institutes and universities, but studies on structural materials based on special electrical and electronic materials are still in the first stage. Particularly, in the case of special materials having excellent structural properties, highly developed countries exclusively produce and sell these materials while avoiding the opening and transfer of related know-how. For this reason, the accumulation of domestic technologies is necessary to develop excellent structural materials.

Currently, formaldehyde-based adhesives, which are used in wooden houses, indoor floors made of wood, and the wood industry, have a limitation on their use in foreign countries due to their carcinogenic risk. Examples of the formaldehyde-based adhesives include urea resin adhesives, melamine resin adhesives, urea- melamine resin adhesives and phenol resin adhesives. Formaldehyde, which is a raw material of adhesives mainly used in the wood industry, is the main cause to generate volatile organic compound (VOC) . Such VOC are emitted from adhesives or boards produced using the same. Thus, since the formaldehyde-based adhesives have the problem of formaldehyde emission, regulations on their use are tightened gradually in the whole world, and currently, plywoods, particle boards and fiber boards, etc., are rated according to the emission of formaldehyde .

Meanwhile, polyurethane adhesives are a material with excellent mechanical, electrical insulating and adhesive properties and superior molding processability, and selected in various ways depending on their use or purpose . To obtain such functional resins, the chemical structure of conventionally used materials is selectively changed such that they have excellent chemical, thermal, electrical and physical properties.

Polyurethane is the general term for polymer materials containing both a urethane bond and a urea bond in their chain. The urethane bond is produced by the reaction of an isocyanate group (-NCO) with a hydroxyl group (-OH) , and the urea bond is produced by the reaction of the isocyanate group with an amine group (-NH₂) . The polyurethane uses polyol as a soft segment and isocyanate as a hard segment. The isocyanates can be broadly classified into aromatic and aliphatic structures, and linear and non-linear structures. The aromatic isocyanate has a higher cohesive energy than the aliphatic isocyanate, and the formed urea bond resulting from the isocyanate has a higher cohesive force and hydrogen bonding strength than the urethane bond, and thus, it shows strong physical cross-linking and increased mechanical properties. However, the polyol contained in the polyurethane has a problem in that its price is expensive.

Disclosure of Invention

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to produce adhesives using fatty acid, glycerol and polyτnethylenebisphenylisocyanate, so that the shortcoming of the prior formaldehyde-based adhesives is overcome, the problem of the high cost of polyols forming the polyurethane adhesives is solved while adhesives having improved adhesive property are provided.

To achieve the above object, the present invention provides adhesives produced by reacting polymethylenebisphenylisocyanate of the following formula (1) with the fatty acid and glycerol obtained by the hydrolysis of vegetable oil, edible oil or waste edible oil : (Formula 1)

wherein n is preferably an integer selected from the range of 1 to 10.

In the adhesives of the present invention, the equivalent weight ratio of the fatty acid : the glycerol : the polymethylenebisphenylisocyanate is preferably in the range of

1:1:1 to 1:1:5, and more preferably 1:1:4. Furthermore, the fatty acid is preferably an unsaturated fatty acid, and more preferably an unsaturated oleic acid

(omega-9 fatty acid; CH₃ (CH₂) ₇CH=CH (CH₂) ₇C0₂H) ) .

The unsaturated fatty acid is a chain compound having an unsaturated carbon-carbon bond and a carboxyl group in one molecule. Particularly, unsaturated fatty acids with an even number of carbon atoms ranging from 12 to 24 are widely found in animals and plants in the form of glycerides, including oleic acid. The unsaturated fatty acid glycerides have a lower melting point than saturated fatty acid glycerides and known as drying oil. In addition, acrylic/methacrylic acid ester that is a lower unsaturated fatty acid is an important unit for polymer synthesis . An oleic acid, which is used in an embodiment of the present invention as the unsaturated fatty acid, is widely found in animals and plants and has one double bond. Particularly, it is contained in olive oil or camellia oil at large amounts, and also contained in the oils and fats of bovine or porcine animals. The polymethylenebisisocyanate is preferably a monomer or polymer having an isocyanate equivalent of 1 to 5.

Such adhesives according to the present invention are used as wood adhesives, industrial adhesives, or adhesives for electric/electronic materials, or for the production of urethane oams.

Using an epoch-making method that can be a new turning point, the present invention aims first to develop environment- friendly adhesives using vegetable oils and then to thermosetting adhesives for application to wood. Generally, vegetable oil that is used as edible oil, such as soybean oil, corn oil or palm oil, is a triacrylglycerol

(glyceride) structure which has glycerol at its main chain and various fatty acids derived from carboxylic acids at its side chain. That is, vegetable oil has three fatty acids bonded to one glycerol by ester linkages. Thus, the present invention aimed to develop a material of high moisture resistance by modifying the chemical structure of vegetable oil using its ability to be hydrolyzed, thus rendering it highly functional

(i.e., hydrophobic) . In the present invention, there is no use of formaldehyde which is used in the prior art. Thus, the toxicity of formaldehyde to the human body can be eliminated and the adhesives can be produced at reduced costs . The present invention provides adhesives having new properties. For this purpose, the carboxyl group (-COOH) of each fatty acid (saturated fatty acid and unsaturated fatty acid) and the hydroxyl group (-OH) of glycerol in vegetable oil are reacted with an isocyanate group to form both a polyamide bond and a polyurethane bond. Such adhesives allows the problem of high cost of the prior urethane resin using isocyanate and polyol to be solved, and also contain an amide bond (-C0-NH-) having a higher hydrogen bonding strength than an urethane bond and thus have improved adhesive strength and water resistance.

In other words, glycerol and carboxylic acid, which were obtained by the hydrolysis of vegetable oil, are reacted with highly reactive diphenylmethane-4, 4 ' -diisocyanate (MDI), as shown in the following reaction scheme. In this reaction, the carboxylic acid forms an amide bond by reaction with MDI, and the glycerol forms a urethane bond by reaction with MDI. The amide and urethane bonds may also be linked to one glycerol molecule together.

CH₂OH

OCN. NCO O R-C-OH CHOH

CH₂OH

(BHJ OrOrOIE) (fi£l B||@)

(β£|0[D|-0|H-?5||&)

Generally, during the reaction of the carboxylic acid with MDI, an unstable polymeric anhydride is formed and the amide bond is then formed while generating carbon dioxide. Since the carboxylic acid acts as an acid catalyst in the step of forming this amide bond, there is an advantage in that other catalysts are not required. If a base is used to increase the nucleophilicity of the glycerol, it is liable to break the polymer chain, resulting in a reduction in crosslinking degree of the polymer. Thus, the use of the base must be avoided. Furthermore, as shown in the following reaction scheme, an acid (H⁺) is released from the carboxylic acid and bonded to N of the isocyanate group (-N=C=0) of MDI to reduce its reactivity (i.e., activation energy) , thereby the promoting the reaction as shown in the following reaction scheme. This suggests that the carboxylic acid acts as both a self-catalyst and an additive involved in the reaction.

This can be confirmed by a fact that upon mixing of the three materials (i.e., fatty acid, glycerol and MDI), the generation of heat occurs. However, it can be found that if MDI is mixed only with glycerol, slow reaction will occur. Also, from the result of adhesion tests for Examples 1-8, it can be found that if MDI is mixed only with the carboxylic acid, the adhesion of the resulting adhesives will be remarkably reduced.

Thus, the adhesives of the present invention can form a hydrogen bond with wood cellulose in a similar manner with a peptide bond of protein, and thus have increased bonding strength. Furthermore, they also show excellent compatibility with a polyurethane resin such that the phase separation at the interface between the two polymers does not occur.

Best Mode for Carrying Out the Invention

The present invention will hereinafter be described in further detail by examples. It will however be obvious to a person skilled in the art that that the present invention is not limited to or by the examples.

In the following Examples 1-7, in order to examine the optimal ratio between fatty acid, glycerol and polymethylenebisphenylisocyanate, adhesives of the present invention were produced while changing the amount of use of polymethylenebisphenylisocyanate in a state where the amount of use of fatty acid and glycerol was maintained at a constant value .

Example 1 As shown in Table 1 below, in order to control the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocyanate to 1:1:0, 280.4 g of oleic acid and 30.7 g of glycerol were put in a 500 ml beaker and mixed in a reactor at 2,500 rpm for 5 minutes. Then, the mixture was stirred with a homogenizer at 20,000 rpm for 10 minutes, to produce an adhesive of the present invention. This adhesive was used immediately for adhesion test. Example 2

As shown in Table 1, in order to control the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocyanate to 1:1:1, 280.4 g of oleic acid and 30.7 g of glycerol were put in a 500 ml beaker and mixed in a reactor at 2,500 rpm for 5 minutes. Then, 130 g of polymethylenebisphenylisocyanate was added to the mixture, and stirred with a homogenizer at 20,000 rpm for 10 minutes, to produce an adhesive of the present invention. This adhesive was used immediately for adhesion test .

Example 3

The procedure of Example 2 was repeated except that 2SO g of polymethylenebisphenylisocyanate was used to control the equivalent weight ratio of oleic acid : glycerol : polymethylenebisphenylisocyanate to 1:1:2 as shown in Table 1 below.

Example 4

The procedure of Example 2 was repeated except that 390 g of polymethylenebisphenylisocyanate was used to control the equivalent weight ratio of oleic acid : glycerol : polymethylenebisphenylisocyanate to 1:1:3 as_. shown in Table 1 below.

Example 5

The procedure of Example 2 was repeated except that 520 g of polymethylenebisphenylisocyanate was used to control the equivalent weight ratio of oleic acid : glycerol : polymethylenebisphenylisocyanate to 1:1:4 as shown in Table 1 below.

Example 6 The procedure of Example 2 was repeated except that 650 g of polymethylenebisphenylisocyanate was used to control the equivalent weight ratio of oleic acid : glycerol : polymethylenebisphenylisocyanate to 1:1:5 as shown in Table 1 below. Example 7

The procedure of Example 2 was repeated except that 780 g of polymethylenebisphenylisocyanate was used to control the equivalent weight ratio of oleic acid : glycerol : polymethylenebisphenylisocyanate to 1:1:6 as shown in Table 1 below.

Table 1

PMDI : polymethylenebisphenylisocyanate

In the following Examples 8-12, adhesives of the present invention were produced while changing the amount of use of fatty acid and glycerol in a state where the amount of use of polymethylenebisphenylisocyanate was maintained at a constant value .

Example 8 As shown in Table 2 below, in order to control the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocyanate to 4:0:4, 1121.6 g of oleic acid was put in a 2,000 ml beaker and stirred in a reactor at 2,500 rpm for 5 minutes. Then, 520 g of polymethylenebisphenylisocyanate was added to the oleic acid, and stirred with a homogenizer at 20,000 rpm for 10 minutes, to produce an adhesive of the present invention. This adhesive was used immediately for adhesion test . Example 9 As shown in Table 2 below, in order to control the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocyanate to 3:0.3:4, 841.2 g of oleic acid and 10.23 g of glycerol were put in a 2,000 ml beaker and stirred in a reactor at 2,500 rpm for 5 minutes. Then, 520 g of polvmethylenebisphenylisocyanate was added to the mixture, and stirred with a homogenizer at 20,000 rpm for 10 minutes, to produce an adhesive of the present invention. This adhesive was used immediately for adhesion test . Example 10

As shown in Table 2 below, in order to control the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocyanate to 2:0.6:4, 560.8 g of oleic acid and 20.47 g of glycerol were put in a 2,000 ml beaker and stirred in a reactor at 2,500 rpm for 5 minutes. Then, 520 g of polymethylenebisphenylisocyanate was added to the mixture, and stirred with a homogenizer at 20,000 rpm for 10 minutes, to produce an adhesive of the present invention. This adhesive was used immediately for adhesion test . Example 11

The procedure of Example 5 was repeated except that 280.4 g of oleic acid and 30.7 g of glycerol were used to control the equivalent weight ratio of oleic acid : glycerol : polvmethylenebisphenylisocyanate to 1:1:4. Example 12

As shown in Table 2 below, in order to control the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocyanate to 0:1.3:4, 40.93 g of glycerol was put in a 500 ml beaker and stirred in a reactor at 2,500 rpm for 5 minutes. Then, 520 g of polymethylenebisphenylisocyanate was added to the glycerol, and stirred with a homogenizer at 20,000 rpm for 10 minutes, to produce an adhesive of the present invention. This adhesive was used immediately for adhesion test. Table 2

PDMI : polymethylenebisphenylisocyanate

In order to examine the adhesion of the inventive adhesives, in the following test example, a plywood panel for adhesion test was prepared and then measured for room temperature adhesion, semi-waterproof adhesion and waterproof adhesion.

Test Example 1 : Preparation of veneer panel

As a veneer panel for preparing a plywood panel for adhesion test, meranti (Dipterocarceae) having a specific gravity of 0.5-0.8 and a moisture content of 6.27% at the outer ply and 5.10% at the core ply was used. The veneer panel had a thickness of 1.0 mm at the outer ply and 2.4 mm at the core ply, and was cut to a size of 200 mm x 200 mm such that a test for plywood preparation could be easily performed. Also, the veneer panel had a moisture content of 6.7% at the outer ply and 6.1% at the core plate. This moisture content was measured according to a test method of KS F 3101. Namely, the moisture content was measured by cutting each of the outer and core plies to a size of 100 mm x 100 mm, drying it in a drier at 105 ± 2 °C for 24 hours, measuring its weight, and then calculating its moisture content according to the following equation (1) :

, , Wa - Wo ,

MC (%)= x 100 (1)

Wo

In the equation (1) , W₀ is the weight of an oven-dried sample and W_a is the weight of an air-dried sample. Test Example 2 : Preparation of plywood panel for adhesion test using inventive adhesives

Plywood panels for adhesion test were prepared using the adhesives of the present invention under conditions given in Table 3 below. Namely, the veneer panels prepared in Test Example 1 was used, and the adhesives produced in Examples 1-12 were applied on the veneer panels with a roller at an application amount of 100 g/m² (one-sided application) in view of the fact that the amount of use of the prior adhesives is 120- 170 g/m² (one-sided application) and the content of moisture in the prior adhesives is less than 1%.

The hot press of the veneer panels was performed using a passive hydraulic cold/hot press (Carver, model 2731, two-stage type, USA, ram diameter: 5.69 cm) . In this hot press step, in view of the attachment phenomenon of metals on cauls and woody boards, a polypropylene film with a melting point of 170-180 °C was used. Table 3 :

Test Example 3 : Adhesion test for plywood panel using adhesives of the present invention

The plywood panel prepared in Test Example 2 was cut to a size of 75 mm x 25 mm to produce a type B sample according to KS F 3101. In order to examine the adhesion of the sample, the sample was measured for room temperature adhesion, semi- waterproof adhesion and waterproof adhesion.

The room temperature adhesion is the adhesion measured at room temperature. The semi-waterproof adhesion is the adhesion measured in a wet sample state after immersing the sample in hot water of 60 ± 3 C° for 3 hours and slowly cooling it in room temperature water. The waterproof adhesion is the adhesion measured in a wet state after boiling the sample in boiling water for 4 hours, drying it a drier of 60 + 3 C° for 20 hours, boiling it in boiling water for 4 hours, and then slowly cooling it in room temperature water.

The adhesion test was performed using a universal material tester (Hounsfield H 50K-S, England) at a crosshead rise speed of 2 mm/min, and the adhesion was calculated according to the following equation (2) :

Ps Tensile - Shear strength (kgf/c ²) = (2)

L x W

In the equation (2) , Ps is the maximum load (kgf) , L is the length (cm) of the sample, and W is the width of the sample.

The measured results are given in Table 4 below.

Table 4 :

From the above results, it can be found that when the amount of fatty acid and glycerol is maintained at a constant value, the adhesion is increased according to an increase in polymethylenebisphenylisocyanate content, but when the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocynate is more than 1:1:4, the adhesion shows a tendency to reduce .

Furthermore, it can be found that when the amount of polymethylenebisphenylisocyanate is maintained at a constant value while increasing the amount of glycerol and reducing the amount of fatty acid, excellent adhesion is obtained, and the most excellent adhesion is obtained when the equivalent weight ratio of equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocynate is 1:1:4.

It is believed that the reason for this increase in adhesion is because an isocyanate group remaining unreacted after reacting the isocyanate group of polymethylenebisphenylisocyanate with the hydroxyl group of glycerol to form a polymer is reacted with the hydroxyl group of wood cellulose while the carboxyl group of the fatty acid used at a suitable amount is reacted with the isocyanate group to form an amide group which forms a hydrogen bond with the hydroxyl group of wood cellulose.

In order to examine the adhesion of conventionally used adhesives, the following comparative examples were carried out in the same manner as the test examples, to measure the room temperature adhesion, semi -water proof adhesion and waterproof adhesion of the conventional adhesives.

Comparative Example 1: Preparation of conventional adhesives

1) Urea resin adhesive

Ammonium chloride (NH₄C1) as a hardening agent was added to a purchased urea resin adhesive at the amount of 10% by weight relative to the solid content of the adhesive, and then mixed with a stirrer at 2,000 rpm, thereby preparing a urea resin adhesive.

2) Melamine resin adhesive

Ammonium chloride (NH₄C1) as a hardening agent was added to a purchased melamine resin adhesive at the amount of 10% by weight relative to the solid content of the adhesive, and then mixed with a stirrer at 2,000 rpm, thereby preparing a melamine resin adhesive.

3) Urea-melamine resin adhesive

A purchased urea resin adhesive was added to a purchased melamine resin adhesive at a weight ratio of 1:1, and then mixed with a stirrer at 1,500 rpm, thereby preparing a urea-melamine resin adhesive . 4) Phenol resin adhesive

A purchased phenol resin adhesive was used intact without adding a hardening agent .

5) Polyurethane adhesive

A polyurethane adhesive was prepared by the reaction of polymethylenebisphenylisocyanate with polyol.

The solid content, pH and viscosity of the conventional adhesives prepared as described above are given in Table 5 below. As shown in Table 5, the pH of the polyurethane adhesive was not measured.

Table 5 :

Comparative Example 2: Preparation of plywood panel for adhesion test using conventional adhesives For comparison, a plywood panel for the adhesion test was prepared using the conventional adhesives under conditions given in Table 6. As the conventional adhesives for comparison, there were used the formaldehyde-based adhesives, such as urea resin, melamine resin, urea-melamine resm and phenol resin adhesives, and the polyurethane adhesive, which had been prepared in Comparative Example 1. The formaldehyde-based adhesives were applied at the amount of 150 g/m³ (one-sided application) in view of the fact that the application amount of the conventional adhesives is in the range of 120 to 170 g/m³ (one-sided application) as described in chapter 3, paragraph 10, item 2 of a test procedure (forestry) provided by Korea Forest Research Institute. The polyurethane adhesive was applied at the amount of 75 g/m³ (one-sided application) . The application of such adhesives was performed with a roller.

The hot press of the panels was performed using a passive hydraulic cold/hot press (Carver, model 2731, two-stage type, USA, ram diameter: 5.69 cm). In this hot press step, in view of the attachment phenomenon of metals on cauls and woody boards, a polypropylene film with a melting point of 170-180 °C was used.

Table 6:

Comparative Example 3 : Adhesion test for plywood panel using conventional adhesives

In order to examine the adhesion of the adhesives prepared in Comparative Example 2, the procedure of Test Example 3 was repeated to measure the room temperature adhesion, semi-water proof adhesion and waterproof adhesion of the conventional adhesives.

The measured results are given in Table 7 below. Table 7

From the above results, it can be found that when the adhesive of the present invention is used at the equivalent weight ratio of fatty acid : glycerol : polymethylenebisphenylisocyanate of 1:1:4, it shows excellent adhesion as compared to the conventional adhesives.

Industrial Applicability

As described above, according to the present invention, the adhesives for the commercially available industrial materials can be produced from the polymethylenebisphenylisocyanate (PMDI) as a raw material of urethane-based adhesives, and the fatty acid and glycerol obtainable from vegetable oils, such that these adhesives can be used as an environment-friendly thermosetting material. The inventive adhesives thus obtained are widely used as wood adhesives, industrial adhesives, or adhesives for electric/electronic materials, or for the production of urethane foams .

Claims

What Is Claimed Is:

1. Adhesives produced by the reaction of polymethylenebisphenylisocyanate of the following formula (1) with the fatty acid and glycerol obtained from vegetable oil, edible oil or waste edible oil: (Formula 1)

2. The adhesives of Claim 1, wherein the equivalent weight ratio of the fatty acid : the glycerol : the polymethylenebisphenylisocyanate is in the range of 1:1:1 to 1:1:5.

3. The adhesives of Claim 2, wherein the equivalent weight ratio of the fatty acid : the glycerol : the polymethylenebisphenylisocyanate is 1:1:4.

4. The adhesives of Claim 1, wherein the fatty acid is an unsaturated fatty acid.

5. The adhesives of Claim 4, wherein the unsaturated fatty acid is an oleic acid (omega- 9 fatty acid; CH₃ (CH₂) ₇CH=CH (CH₂) ₇C0₂H) ) .

6. The adhesives of Claim 1, wherein the polymethylenebisphenylisocyanate is a monomer or polymer having an isocyanate equivalent of 1 to 5.

7. The adhesives of Claim 1 or 6, wherein the n in the formula (1) is an integer selected from the range of 0 to 10.

8. The adhesives of Claim 1, wherein the fatty acid and glycerol are obtained by the hydrolysis of vegetable oil, edible oil or waste edible oil .

9. The adhesives of Claim 1, which are used as wood adhesives, industrial adhesives, or adhesives for electric/electronic materials, or for the production of urethane oams .