EP0788531A1

EP0788531A1 - Polyamides as remoistenable adhesives

Info

Publication number: EP0788531A1
Application number: EP95907982A
Authority: EP
Inventors: Sharf U. Ahmed
Original assignee: HB Fuller Licensing and Financing Inc
Current assignee: HB Fuller Licensing and Financing Inc
Priority date: 1994-09-16
Filing date: 1995-01-05
Publication date: 1997-08-13
Also published as: JPH10507783A; AU691871B2; CA2199813A1; AU1598395A; NZ279381A; WO1996008538A1; EP0788531A4

Abstract

The present invention is a novel remoistenable adhesive and an improvement in the bonding method for an envelope, a stamp, a sticker, a packaging tape or a label using a remoistenable adhesive, wherein the remoistenable adhesive is a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelic acid, azelaic acid, suberic acid and sebacic acid, and an alkyleneoxy diamine component consisting of one or more diamine compounds having the formula: H2N-CyH2y-(OC2H4)x-O-CyH2y-NH2 where y is 2 or 3 and x is 1-50.

Description

POLYAMmES AS REMOISTENABLE ADHESIVES

Background of the Invention The present invention pertains to remoistenable hot melt adhesives, and their application to envelopes, stamps, packaging tape or stickers and labels.

To be water-moistenable, an adhesive composition must be activatable by moistening with water. The adhesive composition is a bonding agent which may be applied to one surface utilizing a hot melt technique and another surface using a water-moistening technique, so that the two surfaces are bonded together by means of composition. By way of example, such a composition may be applied by the hot melt technique as gumming for stickers and labels, stamps, packaging tapes and envelope flaps at a point of manufacture where the intricate equipment required for hot melt application is available, the stickers and labels, stamps, packaging tapes and envelope flaps, ultimately being applied by the consumer to other surfaces using the much simpler water-moistening technique, e.g. by moistening the adhesive coating prior to application to the other surface. The hot melt application is utilized where the required equipment is available because it is a rapid and economical technique, the water-moistening technique is utilized precisely because it doesn't require such elaborate equipment. Overall, remoistenable adhesives are valued because of their superior process speed, and their streamlining of process equipment by elimination of driers and other auxiliary equipment or the like.

In attempting to provide a single adhesive composition which is to be applied to one surface using a hot melt technique and another surface using a water- moistening technique, considerations arise which are not present in the provision of an adhesive composition to be applied by either technique alone. For example, most water-moistenable adhesives do not possess the requisite thermoplastic properties permitting hot melt application of desirably smooth glossy coats thereof. Similarly, most hot melt applicable thermoplastic adhesives are water insensitive and cannot be readily tackified by water-moistening. Moreover, such adhesive compositions must obviously be heat-tackifiable to be applied by hot-melt techniques and also moisture- tackifiable to form bonds by water-moistening techniques. On the other hand, once the composition has been hot-melt applied to a substrate, it must be able to resist elevated temperature conditions likely to be found in its environment without again becoming tackified or undergoing other undesirable changes, such as discoloration (darkening), over a prolonged period of time. Similarly, it must be able to withstand the various humid conditions likely to be found in its environment without becoming tacky until it is actually moistened immediately prior to use.

The tendency of the adhesive to undergo premature sealing is a problem not yet fully remedied by the prior art. Under humid conditions this adhesion is measured in terms of the humidity blocking resistance at a given relative humidity (under a given load at a given temperature, for a given period of time). The blocking resistance is normally measured in terms of the percentage tear occurring, with high levels of blocking producing high level of tear when the adhesive-bearing substrate is removed from the opposed surface. It is desirable to have a remoistenable adhesive that resists blocking in extreme heat and humid conditions. Traditionally, non-block additives such as petroleum and synthetic waxes and fatty amines have been incorporated into the polyamide to prevent blocking problems. Typical of these are Acrawax C, a 140°-143° C melt point synthetic wax from Glyco Chemicals, erucyl amide, oleyl amide, N.N ethylenebisoleamide and the like.

Remoistenable water soluble polymers other than polyamides appear to be deliquescent, that is they tend to undergo gradual dissolution and liquefaction by the attraction and absorption of moisture from the air, causing them to block at high humidity and temperature. This can cause a serious problem during storage of products utilizing remoistenable adhesives. Blocking can be characterized as any degree of adhesive between touching layers of similar or dissimilar material, such as occurs under moderate pressures during storage or use. To achieve desired properties prior art polymers require wax and tackifiers to prevent blocking and to promote stability. The end result is that remoistenable adhesive products that suffer from blocking are rendered useless when they prematurely seal. Water soluble polymers like poly vinyl alcohol, PeOX, and PVP are known in literature for their compounding ability to form adhesives for remoistening application. These hot melt adhesives provide several advantages for the envelope and packaging industries and other related industries, including a very fast rate of application, the ability to heat seal when remoistening is not required, and the fact that the water solubility of the adhesive will make the products recyclable. However, these water soluble polymers require water soluble/insoluble tackifiers and waxes to achieve the desired remoistening properties. Because of the nature of the polymers and the use of tackifiers and waxes the adhesives are rendered with low blocking resistance and low thermal stability.

Flanagan, U.S. 4,623,688, discloses remoistenable hot melts adhesives which are prepared from poly(alkyloxazoline) (having the general formula C₃H₄NO), a diluent and, optionally, a tackifier, plasticizer and non-block additive. Like other known remoistenable adhesives, in order to achieve preferred non- blocking, heat and humidity resistance, and bond strength properties certain materials are added, such as tackifiers, plasticizers, stabilizers and non-block additives.

U.S. patents 4,623,688; 5,053,484; 4,133,803; 5,086,162 all teach the synthesis of water soluble polyamides. Poly amides have been produced for many reasons, but not for use as a remoistenable adhesive. Klein, U.S. 4,133,803, discloses polyoxypropylene polyamine polyamide thermoplastic adhesives. It pertains to a novel thermoplastic adhesive comprised of a polyamide product, and can be prepared from relatively inexpensive and readily available synthetic materials. This invention was driven by the need for satisfactory replacements for naturally derived materials. It eliminated the need for employing vegetable or animal-based dimer or trimer fatty acids which are usually in short supply, but did not disclose the use of the polyamides as a remoistenable adhesive.

Speranza, U.S. 5,086,162, also disclosed water soluble polyether amides produced by reacting poly alky lene glycol diamine with dicarboxylic acids. The object of the invention was to provide novel polyether amides with terephthalamide units having improved water absorbency, and/or which are soluble in water. The patent provided a plurality of easily implemented methods for making these novel materials. Uses for these novel polyamides include applications where good water absorption is desired, such as fabrics, where it is known that some incorporation of moisture is useful in reducing tenancy of the fabric to carry an undesirable static charge. The patent also teaches that the polyamides can be used for hot-melt adhesives, but the patent does not disclose or suggest the usefulness of the polyamide as a remoistenable adhesive.

Speranza, U.S. 5,053,484, discusses polyether amides from mixtures of polyether diamines and dicarboxylic acids. The amides are water soluble, and may also be used for hot melt adhesives. The purpose of the invention was to increase solubility, and provide easily implemented methods of making these polymer materials. This piece of prior art also fails to disclose the polyamide as a valuable remoistenable adhesive.

Summary of the Invention

The invention is directed to remoistenable hot melt adhesives which are the product of a dicarboxylic acid selected from the group consisting of adipic acid, pimelitic acid, azelaic acid and suberic acid, and a polyoxyalkylene diamine. This polyamide is characterized by the properties of a remoistenable adhesive and an outstanding balance of non-block characteristics under heat and high humidity conditions combined with excellent bond strength without the aid of wax, tackifiers or antioxidants and is an improvement over the prior art.

This invention is an improvement over known remoistenable adhesives used in the envelope and packaging industry and other related industries, and is also a novel use for known polyamide hot melts. These polyamides, though having water soluble tendencies, are also remoistenable in nature, and provide superior bonding and are resistant to high temperature and high humidity. Unlike prior remoistenable adhesives, the additions of additives such as waxes, tackifiers and antioxidants are not required to prevent blocking and to promote stability in high heat and humidity. Thus the present invention provides an improvement to the stability of the remoistenable adhesive in severe conditions, and at the same time provides a new use for polyamides.

In one aspect the invention is an improvement in the bonding method of an envelope in which an envelope, having a folding closure flap and having a film of remoistenable adhesive applied thereto, is stored for a period of time, after such time the remoistenable adhesive is moistened, and the flap is folded over onto the envelope and pressed against the envelope until bonded, the improvement comprising that the remoistenable adhesive is a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelic acid, azelaic acid and suberic acid, and an alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C^_2y-(OC₂H₄)_ll-O-C_yH_?y-NH₂ where y is 2 or 3 and x is 1-50.

Brief Description of the Drawings

Fig. 1 is a rear view of an open envelope in accordance with the present invention illustrating the application of the remoistenable adhesive; and

Fig. 2 is a rear view of a closed envelope in accordance with the present invention illustrating the utility of the remoistenable adhesive.

Detailed Description of the Invention

This invention is a novel remoistenable adhesive and a new use of thermoplastic polyamides as remoistenable adhesives for their application in the packaging and envelope industry and other related industries, such as application to envelopes, stamps, packaging tape or stickers and labels. Unlike prior remoistenable adhesives, polyamides such as these do not require the use of waxes, tackifiers and antioxidants to prevent blocking and to promote thermal stability in high heat and humidity. These thermoplastic polyamides are generally prepared using a dicarboxylic acid selected from the group consisting of adipic acid, pimelitic acid, azelaic acid and suberic acid, and alkyleneoxy diamines. The typical formula comprises adipic acid and TTD diamine in exact stoichiometric ratio. However, products made from adipic acid in conjunction with stearic acid, benzoic acid or sebacic acid and the TTD diamine also showed the remoistening property. Low to high viscosity polyamides can be made for remoistening application by changing the ratio of the acid and amine. Waxes and/or tackifiers are not necessary to show the remoistenable property in the present invention as they are in known remoistenable adhesives, but may be used in certain situations to increase the blocking resistance and thermal stability.

Although certain U.S. patents teach the synthesis of water soluble polyamides, such as the ones that are the subject of the present invention, none describe the remoistenable properties of the polyamides. These hot melt adhesives provide several advantages for envelope and packaging industries and other related industries, including a very fast rate of application, the ability to heat seal when remoistening not required, and the water solubility of the adhesive will make the product recyclable. Water soluble polymers known in the prior art require water soluble/ insolubly tackifiers and waxes to achieve the desired remoistening properties. Because of the nature of the prior art polymers and the use of tackifiers and waxes the adhesives are rendered with low blocking resistance and low thermal stability. Polyamides show no need of tackifiers and waxes to achieve high blocking resistance and high thermal stability, and can be made without the process of formulation.

Polyamides have been produced for many reasons, but not for use as a remoistenable adhesive. Some polyamides were created in response to a need for satisfactory replacements for naturally derived materials, and can be prepared from relatively inexpensive and readily available synthetic materials. Water soluble polyether amides produced by reacting polyalkylene glycol diamine with dicarboxilic acids were created to provide novel polyether amides with terephthalamide units having improved water absorbency, and/or which are soluble in water. It also was a purpose of past polyamide inventions to provide a plurality of easily implemented methods for making these novel materials. Still, this product has not been recognized for its usefulness as a remoistenable adhesive. The present invention takes all these economic and efficient advantages of polyamides and utilizes them in a novel way as remoistenable adhesives. Figs. 1 & 2 illustrate an application for the improvement in the bonding method for closing an envelope wherein the remoistenable adhesive used is a polyamide. In the illustration, an open envelope, generally designated 10, as shown in Fig. 1, having a folding closure flap 2, has a film of remoistenable adhesive 4 applied thereto. The envelope can be stored for a period of time, after which the remoistenable adhesive 4 is moistened, usually by licking the adhesive, and the flap 2 is folded over along the crease point 3 onto the back face 6 of the envelope and pressed against the envelope until a bond 8 is created. The end result is a sealed envelope 20 as shown is Fig. 2. This application is only an example of the use of polyamides as remoistenable adhesives. Other applications include applying the adhesive to either the closure flap 2 or the back face 6 of the envelope or both, and/or using other envelope type products. The adhesive can be used in a similar manner in conjunction with other forms of packaging material, such as packing tape and the like.

Polyamides made from adipic acid and TTD (3, 3 (diethylene trioxy) bispropylamine) diamine have been described in U.S. patent 3,883,090 for various applications, and several other U.S. patents (patent numbers 4,623,688; 5,053,484; 4,133,803; 5,086,162) describe the synthesis of water soluble polyamides using oxyethylene or oxypropylene diamines. These patents disclose that polyamides can be used as hot melt adhesives, but they do not describe or infer the remoistenable property of the polyamide.

Other water-dispersable polyamides can be prepared by reacting adipic acid with a diamine, such as polyethylene glycol diamines, like triethylene glycol diamine (Jeffamine^® EDR-148) or tetraethylene glycol diamine (Jeffamine^® ER-192) or a combination of the two diamines. A combination of these higher diacids with adipic acid can produce water-soluble or water-dispersible polyamides. Increasing the amount of higher carbon diacids in conjunction with adipic acid results in polyamide with decrease in solubility. However, this can be compensated by increasing the EO (ethylene oxide) content of a portion of the polyethylene glycol diamine component. Jeffamine* ED 600, ED 900, ED 2000, D-230, D-400 and D- 2000 are examples of higher EO content polyoxyalkylene diamines which may be employed. Thus, in particular, Dimer Acid can be used in combination with adipic acid when triethylene glycol diamine or tetraethylene glycol diamine are employed in combination with the polyoxyalkylene diamines Jeffamine* ED 600 or D-400.

The preferred elements in the general reaction are adipic and TTD

Diamine. It is most preferable to add stearic acid, benzoic acid or sometimes sebacic acid, to the reaction to increase the solubility. The reaction of TTD and adipic acid should be used in equal stoichiometric ratio, however, for reaction between adipic acid, TTD, and sebacic acid the limit of sebacic can be between 0- 25% . For the reaction of TTD, adipic acid, and stearic acid the limit of stearic acid can be 0-15%.

The remoistening adhesives have many applications and can be used in the envelope industry as well as in the packaging industry for paper tapes as remoistenable paper tapes. In addition, the water solubility of the adhesive provides a completely repulpable tape for packaging application and is thus recyclable. The hot melt adhesives used in the invention are able to maintain adequate bond strength so that in warm temperatures the seal is not jeopardized. The polyamides display excellent humidity resistance, high thermal stability and showed good blocking resistance at high temperature and high humidity without the aid of tackifiers, waxes or formulation. Some of the polyamides tend to have slow set time, but this can be decreased by using some fast setting waxes.

The present invention is advantageous over the prior art/background technologies in that they resist blocking at high humidity and temperature. The polyamides employed in the invention do not require these additional materials to achieve these desirable properties.

While the remoistenable adhesives of the invention may be made solely from mixtures of diamines and mixtures of diacids which also showed remoistenable properties, in some cases in order to achieve a particular property for certain applications or to reduce the cost of the adhesive the polyamides may be optionally formulated with waxes, tackifiers, antioxidants, melt viscosity modifiers, and the like, provided that the additives do not themselves adversely affect the water dispersability of the adhesive formulation.

Although the formulated products also showed water solubility /dispersibility and remoistenability properties, to achieve certain desired levels tackifiers, waxes and antioxidants may be used to extend the adhesive properties of the system. Suitable tackifiers are (1) natural and modified rosins such, for example, as gum rosin, wood rosin, tall-oil resin, distilled rosin, hydrogenated rosin, dimerized rosm, and polymerized rosin, (2) polyterpene resins having a softening point, as determined by ASTM method E28 58T, of from about 60° to 140° C, the latter polyterpene resins generally resulting from the polymerization of terpene hydrocarbons, such as bicyclic mono-terpene known as pinene in the presence of Friedel-Crafts catalysts at moderately low temperature, (3) phenolic-modified terpene resins such, for example, as the resin product resulting from the condensation in an acidic medium, of a bicyclic terpene and a phenol; (4) aliphatic petroleum hydrocarbon resins having a Ball and Ring softening point of from about 60° to 140°C, the latter resins resulting from the polymerization of monomers consisting primarily of olefins and diolefins, (5) glycerol and pentaerythritol; (6) esters of rosin or modified rosin; (7) styrene resins and modified styrene resins; (8) hydroabietyl alcohol and the phthalate ester thereof; and (9) aliphatic, aromatic and aliphatic/aromatic copolymers and their hydrogenated counterparts. These tackifying resins are present usually in an amount of about 5 to 40% by weight of the adhesive.

Antioxidants or stabilizers which may be employed in remoistenable hot melt compositions include phenolics, amines, and quinones or the like. Especially useful are the high molecular weight hindered phenols and multifunctional phenols such as sulfur and phosphorous-containing phenols. Hindered phenols are well known to those skilled in the art and may be characterized as phenolic compounds which also contain bulky radicals in close proximity to the phenolic hydroxyl group thereof. In particular, tertiary butyl groups generally are submitted onto the benzene ring in at least one of the other positions relative to the phenolic hydroxy group. The presence of these substituted radicals in the vicinity of the hydroxyl group serves to retard its stretching frequency and correspondingly, its reactivity. This steric hindrance thus provides the phenolic compound with its stabilizing properties.

The polyamides of the present invention show the ability of absorbing moisture without becoming deliquescent. Deliquescent is the tendency to undergo gradual dissolution and liquidefaction by the attraction of moisture from air. Although the polyamides absorbed 30% moisture they were not deliquescent, in fact they desorbed after sitting in ambient conditions. Polymers normally used as remoistenable adhesives like PeOX are deliquescent (tending to undergo gradual dissolution and liquefaction by the attraction of moisture from air) and stays in that form even when they are removed from high humidity. This characteristic causes them to block at high humidity and temperature. To determine if the polyamides are deliquescent a moisture absorption test was administered and is explained below.

Examples:

Typical reactions that are the subject of the invention are shown below, but the present invention is not limited to these alone, nor does the invention preclude any similar applications or substitutes:

1) Adipic acid + TTD Diamine = polyamide;

2) Adipic acid + Stearic acid + TTD Diamine = polyamide;

3) Adipic acid + Jeffamine EDR-192 = polyamide;

4) Adipic acid + Jeffamine EDR 148 = polyamide;

5) Adipic acid + Jeffamine EDR 148 -I- D-230 = polyamide; 6) Adipic acid + Jeffamine EDR 148 + D-230 + sebacic acid = polyamide;

7) Polyamide from equation 1 -I- wax + tackifiers = formulated polyamide; and

8) Polyamide from equation 5 + wax = formulated polyamide.

Compound Descriptions:

TTD - H₂N-(CH₂)₃-O-CH₂-CH₂-O-CH₂-CH₂-O-(CH₂)₃-NH₂ EDR-192 - H₂N-CH₂-CH₂-(O-CH₂-CH₂)₃-NH₂ EDR-148 - H₂N-CH₂-CH₂-(O-CH₂-CH₂)₂-NH₂ Jeffamine D-230 - NH₂-CH-CH₂-[O-CH₂-CH]_z-NH₂

CH₃ CH₃

Adipic acid (hexane dioic acid) - HOOC-(CH₂)₄-COOH

Sebacic acid - HOOC-tCH^-COOH Stearic acid (Octadeacnoic acid) -

The polyamides employed in the invention may be prepared as described in Example 1 of U.S. 3,882,090. Modifications of the recipe given below for illustrative purposes only, it being understood that those skilled in the art can readily modify the recipes without departing from the invention hereof:

Parts bv Weight

(1) Adipic Acid 146.14 Triethylene Glycol Diamine 148.0

(2) Adipic Acid 146.14 Tetraethylene Glycol Diamine 192.0

(3) Adipic Acid 146.14 TTD¹ Diamine 220.3

¹ 4,7,10-trioxatridecane-l, 13-diamine

Polyamide melt viscosity can be controlled by adding small amounts, typically less than 5%, preferably 0.5-2.5% based on total acid weight of monoacids such as stearic or benzoic acid. An example recipe is given below:

(4) Adipic Acid 145.4 Stearic Acid 2.7 TTD Diamine 220.3

Elements such as adipic acid, diamine, stearic acid, benzoic acid, and sebacic acid enhance the water solubility of the adhesive. Non-essential elements such as wax, tackifiers and antioxidants contribute properties that are lacking in particular situations. Wax increases setting/lowering the set time/filler, tackifiers help tackiness and antioxidants allows use at high temperature without degradation.

Experiments were run to determine and verify the herein asserted characteristics and nature of polyamides as remoistenable adhesives. The results are shown below and indicate that polyamides, when used as remoistenable adhesives, display an outstanding balance of non-block characteristics under high heat and high humidity conditions combined with excellent bond strength without the aid of wax, tackifiers or antioxidants.

In the moisture absorption test of NP-2068 (parts by weight: adipic acid 145.4; stearic acid 2.7; and TTD Diamine 220.3), the batch of NP-2068 was drawn to film for the test. Four strips of paper were cut and weighed and placed in a desiccator at 55-60% humidity and room temperature of 70-75°F. A second set were placed at room temperature in a desiccator with water at the bottom at 70-75 °F with a relative humidity at 95-98%. After 16 hours, the samples were weighed and left out in ambient conditions. There was an initial tackiness, but after 24 hours, they were weighed and displayed a lower weight, thus evidencing desorbing of moisture. This desorbing quality helps the sample to resist blocking. The results of the absorbency testing are shown below in Table #1 :

Table #1 : Water absorption/desorption data

NP-2068 Sample Wt. after % Water Wt. in g. % Water % Water wt. in g. 16 hrs. absorp¬ at RT in sample desorbed in tion and 50-

RT/90- 55% RH 95% RH for 24 hrs.

Sample 0.589 0.769 30.6 0.604 1.5 29.1

A

Sample 0.451 0.597 32.4 0.459 1.7 30.7

B

RT = Room Temperature RH = Relative Humidity NP-2068 = parts by weight: adipic acid 145.4; stearic acid 2.7; and TTD Diamine 220.3 (samples A & B are separate samples of NP- 2068).

To determine the polyamides non-blocking capabilities and its thermal stability, three test were run on 9 different samples of various mixtures of polyamides: (1) A remoistenability test 24 hrs; (2) A blocking test at 140° for 24 hrs; and (3) A 84% or 93% humidity resistance test for 24 hrs. The results of these tests were employed to distinguish polyamides from formerly used remoistenable adhesives, illustrating polyamides improvement over the prior art.

The test to determine the remoistenability of hot melt adhesives is used to determine whether a remoistenable hot melt adhesive, after initial application, gives adequate bonding when remoistened and mated to a particular substrate. In this particular test, the sample is heated to 300°F. A sheet of paper is taped down on which the adhesive is drawn down with a metal draw down bar. The adhesive is allowed to cool. After which the paper is cut into 1/2" strips with a thickness of between .6 mil. and 1 mil. These strips are allowed to sit at low humidity (50%) for two hours. The strips are moistened with room temperature water and immediately pressed onto a second piece of bond paper with medium finger pressure as if you were sealing an envelope. This test is done with various levels of moisture applied for each adhesive, noting the amount applied as little, medium, or heavy moisture on each strip. The sealed strips are placed in low humidity (50%) environment for 24 hours. After which the strips are pulled from the bond paper recording fiber tear observed. A side by side comparison done by performing a test within adhesive lot showed to have excellent remoistenability along with the test sample is important. Also be sure to alternate the test and known sample strips with moistening and bonding to the substrate to insure comparable amount of moisture is applied to each adhesive type. The percent of fiber tear is rated as excellent (40% or more), good (10% - 40%), or poor (less than 10%). An adhesive has passed if at least one third of the heavily or moderately moistened strips have excellent or good fiber tear ratings. The test sample must perform as well or better than the controlled to pass this test. The results of this test as applied to the nine samples are illustrated in Table #2.

The test to determine the blocking potential of hot melt adhesives is used to determine whether remoistenable hot melt adhesive, after initial application, will have undesirable blocking characteristics under pressure and heat. The procedure for this test is the same as the remoistenability test up to the point where the strips of paper are allowed to stand in low humidity for two hours. After this step, the strips of the control and the strips of the test adhesive are placed on a tray, adhesive side up. A strip of dried bond paper is placed on top of each adhesive strip. A 100 gram weight is placed on top of each strip, and the tray is placed in a 120° oven for 24 hours. Another tray of specimens is placed in room temperature for 24 hours also. After the 24 hours, the strips are observed noting the degree of adhesive sticking or picking to the plain bond paper that was placed on top of the adhesive area. A side by side comparison is done by performing a test with an adhesive lot shown to have excellent blocking resistance. The degree of picking is rated as excellent (no picking, paper falls away without having to pull the paper), good (very slight picking), okay (significant picking but no fiber tear) or poor (fiber tear of the bond paper is in evidence). When the adhesive has passed at least five or six strips of excellent or good pick rates. The adhesive fails if there are any specimens with a "poor" . The test sample must perform as well or better than the controlled to pass the test. The results of this test as applied to the nine samples are illustrated in Table #2. The humidity resistance test is set up exactly like the blocking test, where one set of strips is placed in 84% humidity for 24 hours and one set of strips is placed in 94% humidity for 96 hours. The results of this test as applied to the nine samples are illustrated in Table #2.

«n 4577-76 = 36.31% Adipic acid, 58.04% TTD Diamine, 4.16% Stearic acid & 1.49% Irganox 1098 (antioxidant).

4358-74 = 42.97% Adipic acid, 21.75% EDR 148, 33.81 % Jeffamine D- 230 & 1.47% Irganox 1098 (antioxidant).

4358-68 = 44.71 % Adipic acid, 29.89% EDR 148, 23.93% Jeffamine D- 230 & 1.47% Irganox 1098 (antioxidant).

While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated.

Claims

What is claimed is as follows:

1. An improvement in the adhesive bonding method for a first substrate, which is an envelope portion, a stamp, a sticker, a packaging tape or a label, in which said first substrate has a film of remoistenable adhesive applied thereto, said first substrate is stored for a period of time, after such time the remoistenable adhesive is moistened, the substrate is joined to a second substrate and pressure is applied thereto until bonded, the improvement comprising that the remoistenable adhesive is a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelic acid, azelaic acid, suberic acid and sebacic acid, and an alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C_yH_2y-(OC₂H₄).-O-C_yH_2y-NH₂ where y is 2 or 3 and x is 1-50.

2. A method as in claim 1 wherein the remoistenable adhesive consists essentially of the thermoplastic polyamide.

3. A method as in claim 1 wherein the acid component consists essentially of adipic acid and stearic acid, and the alkyleneoxy diamine component has the formula:

H₂N-(CH₂)₃-O-CH₂-CH₂-O-CH₂-CH₂-O-(CH₂)₃-NH₂.

4. A method as in claim 1 wherein the acid component comprises adipic acid.

5. A method as in claim 4 wherein the alkyleneoxy diamine component has the formula:

H₂N-(CH₂)₃-O-CH₂-CH₂-O-CH₂-CH₂-O-(CH₂)₃-NH₂.

6. A method as in claim 5 wherein the acid component further comprises a monofunctional carboxylic acid.

7. A method as in claim 6 wherein the monofunctional carboxylic acid is chosen from a group consisting of stearic acid and benzoic acid.

8. A method as in claim 4 wherein the alkyleneoxy diamine component has the formula

H₂N-CH₂-CH₂-(O-CH₂-CH₂)_x-NH₂ where X ranges from 2 to 3.

9. A method as in claim 8 wherein X is 2, and wherein the alkyleneoxy diamine component further comprises a compound having the formula

NH₂-CH-CH₂-[O-CH₂-CH]_z-NH₂ CH₃ CH₃ where Z ranges from 2 to 6.

10. A method as in claim 9 wherein the acid component further comprises azelaic acid and sebacic acid.

11. A method as in claim 1 wherein the remoistenable adhesive further comprises at least one of a wax, an antioxidant and a tackifier.

12. A method as in claim 1 wherein the remoistenable adhesive further comprises at least two of a wax, an antioxidant and a tackifier.

13. A method as in claim 1 wherein the remoistenable adhesive further comprises a wax, an antioxidant and a tackifier.

14. A method as in claim 1 wherein said first substrate is the stamp.

15. A method as in claim 1 wherein said first substrate is the packaging tape.

16. A method as in claim 1 wherein said first substrate is the sticker or label.

17. An envelope, stamp, packaging tape, label or sticker having a film of remoistenable adhesive applied thereto, wherein the remoistenable adhesive comprises a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelic acid, azelaic acid, suberic acid and sebacic acid and a alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C H₂,-(OC₂H₄)_x-O-C_yH₂,-NH₂ where y is 2 or 3 and x is 1-50.

18. An envelope, stamp, packaging tape, label or sticker as in claim 17 wherein the remoistenable adhesive consists essentially of the thermoplastic polyamide.

19. An envelope, stamp, packaging tape, label or sticker as in claim 17 wherein the acid component consists essentially of adipic acid and stearic acid, and the alkyleneoxy diamine component has the formula:

H₂N-(CH₂)₃-O-CH₂-CH₂-O-CH₂-CH₂-O-(CH₂)₃-NH₂.

20. An envelope, stamp, packaging tape, label or sticker as in claim 17 wherein the acid component is adipic acid.

21. An envelope, stamp, packaging tape, label or sticker as in claim 20 wherein the alkyleneoxy diamine component has the formula

H₂N-(CH₂)₃-O-CH₂-CH₂-O-CH₂-CH₂-O-(CH₂)₃-NH₂.

22. An envelope, stamp, packaging tape, label or sticker as in claim 21 wherein the thermoplastic polyamide further contains a monofunctional carboxylic acid.

23. An envelope, stamp, packaging tape, label or sticker as in claim 22 wherein the monofunctional carboxylic acid is chosen from a group consisting of stearic acid and benzoic acid.

24. An envelope, stamp, packaging tape, label or sticker as in claim 20 wherein the alkyleneoxy diamine component has the formula H₂N-CH₂-CH₂-(O-CH₂-CH₂)_x-NH₂ where X ranges from 2 to 3.

25. An envelope, stamp, packaging tape, label or sticker as in claim 24 wherein

X is 2, and wherein the thermoplastic polyamide further comprises a compound having the formula

NH₂-CH-CH₂-[O-CH₂-CH]_z-NH₂ CH₃ CH₃ where Z ranges from 2 to 6.

26. An envelope, stamp, packaging tape, label or sticker as in claim 25 wherein the remoistenable adhesive further comprises sebacic acid.

27. An envelope, stamp, packaging tape, label or sticker as in claim 17 wherein the remoistenable adhesive further comprises at least one of a wax, an antioxidant and a tackifier.

28. An envelope, stamp, packaging tape, label or sticker as in claim 17 wherein the remoistenable adhesive further comprises at least two of a wax, an antioxidant and a tackifier.

29. An envelope, stamp, packaging tape, label or sticker as in claim 17 wherein the remoistenable adhesive further comprises a wax, an antioxidant and a tackifier.

30. An envelope having a folding adhesively bondable closure flap, and having a film of remoistenable adhesive applied thereto, wherein the remoistenable adhesive comprises a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelitic acid, azelaic acid and suberic acid, and a alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C,H_2y-(OC₂H₄).-O- H₂ -NH₂ where y is 2 or 3 and x is 1-50.

31. A stamp having a film of remoistenable adhesive applied thereto, wherein the remoistenable adhesive comprises a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelic acid, azelaic acid and suberic acid, and a alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C_yH_2y-(OC₂H₄),-O-C_yH₂ -NH₂ where y is 2 or 3 and x is 1-50.

32. A packaging tape having a film of remoistenable adhesive applied thereto, wherein the remoistenable adhesive comprises a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelic acid, azelaic acid, suberic acid and sebacic acid, and a alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C^I₂ -(OC₂H₄)_x-O-C H_2y-NH₂ where y is 2 or 3 and x is 1-50.

33. A sticker or label having a film of remoistenable adhesive applied thereto, wherein the remoistenable adhesive comprises a hot melt consisting of a thermoplastic polyamide prepared from an acid component sele6ted from the group consisting of adipic acid, pimelic acid, azelaic acid, suberic acid and sebacic acid, and a alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C_yH_2y-(OC₂H₄)_x-O-C H₂ NH₂ where y is 2 or 3 and x is 1-50.

34. An improvement in the bonding method for closing an envelope in which an envelope, having a folding closure flap and having a film of remoistenable adhesive applied thereto, is stored for a period of time, after such time the remoistenable adhesive is moistened, and the flap is folded over onto the envelope and pressed against the envelope until bonded, the improvement comprising that the remoistenable adhesive is a hot melt consisting of a thermoplastic polyamide prepared from an acid component selected from the group consisting of adipic acid, pimelic acid, azelaic acid, suberic acid and sebacic acid, and an alkyleneoxy diamine component consisting of one or more diamine compounds having the formula:

H₂N-C_>H_2y-(OC₂H₄).-O-C H₂,-NH₂ where y is 2 or 3 and x is 1-50.