WO2009014924A1

WO2009014924A1 - Hot melt adhesive

Info

Publication number: WO2009014924A1
Application number: PCT/US2008/069910
Authority: WO
Inventors: Valmir Aparecido De Mattos Felippe
Original assignee: 3M Innovative Properties Company
Priority date: 2007-07-24
Filing date: 2008-07-14
Publication date: 2009-01-29
Also published as: BRPI0703309A2

Abstract

This disclosure refers, in a general sense, to hot melt adhesives used in industrial applications, such as cardboard boxes, plastic, parts, bookbindings, manufacture of furniture and for application on packaging for frozen food. The embodiment comprises a resin, an oligomer (wax) with a softening point between 100 and 120°C and an ethylene and vinyl acetate copolymer (EVA), possessing, in one embodiment, a vinyl acetate content equal or superior to 28% and a melt flow index equal or superior to 800g/10 min. In some embodiments, the hot melt adhesive of this disclosure has a softening point between 100 and 115°C; thus, when the application temperature of the adhesive of the present disclosure ranges between 120-140°C, the difference between the application temperature of the product and its softening point is between 20 and 30°C.

Description

HOT MELT ADHESIVE

TECHNICAL FIELD

[0001] This disclosure refers, in a general sense, to a hot melt adhesive. More specifically, the disclosure refers to a hot melt adhesive with a low application temperature, comprising a resin, an oligomer (wax) and an ethylene and vinyl acetate copolymer.

BACKGROUND

[0002] Hot melt adhesives are, generally, thermoplastic adhesives commercialized in solid form (as, for example, in the form of a cylindrical stick) for subsequent melting and application through the use of hot glue guns specifically designed for this kind of material.

[0003] Hot melt adhesives are generally composed of three components: a polymeric resin, a tackifier and a wax, as described in Patent Application US2003229168. The polymeric resin is responsible for the cohesive and adhesive properties of the hot melt adhesive and generally comprises from about 25 to about 50 percent in weight of the embodiment.

[0004] Hot melt adhesives are versatile and widely used in industrial applications, such as bookbindings, cardboard boxes, plastic parts and wooden articles, among others. They are generally 100% solid adhesives with application temperatures which vary from about 150 to about 18O⁰C, typically between about 160 and about 17O⁰C (adhesives with high application temperature) and about 120 and about 14O⁰C (adhesives with low application temperature).

[0005] Adhesives with high application temperature generally present higher adhesive and cohesive forces, considering that more energy is needed to disentangle the chains of the polymer resulting in its melting. Low temperature application adhesives are generally used for more sensitive and delicate applications, such as applications to fabric.

[0006] Hot-melt-type adhesives with low temperature application generally possess a softening point ranging form 70 to 8O⁰C. Embodiments of such adhesives are exemplarily described in U.S. Patents Nos. 6,319,979, 6,107,430, 4,749,739. The low softening point of such embodiments derives from the use of amorphous alpha-olefms or waxes with low softening points (less than 72⁰C), considering that it is the raw material which mainly contributes to this property.

[0007] Other examples of hot-melt-type adhesives were described in Patent Applications US2003229168 and US2006116459.

[0008] Another reference in the field is U.S. Patent 3,560,420, which describes a hot melt thermoplastic adhesive characterized by high performance and low cost, which is obtained by the mixture of polyethylene of low molecular weight, phenolic resin, esther of abietic acid, terpene, resin, and ethylene and vinyl acetate copolymer.

[0009] U.S. Patent 4,749,739 describes the incorporation of a synthetic polyethylene wax, a hydrocarbon tackifier and an amorphous polypropylene polymer to create an adhesive of low viscosity.

[0010] Examples of hot melt embodiments based on amorphous alpha-(poly)olefms and low application temperatures are described in US 6,319,979, US 6,107,430, US 4,749,739, EP 0912646, EP 0886656, EP 0564596, and in patent applications WO 9803603 and WO 9733921.

SUMMARY

[0011] This disclosure refers to hot melt adhesives useful in industrial applications, such as cardboard boxes, plastic, parts, bookbindings, manufacture of furniture and for application in packaging for frozen foods.

[0012] More specifically, this disclosure relates to a hot melt adhesive with low application temperature, comprising a resin, a polyethylene oligomer of low molecular weight (also known as polyethylene wax) and an ethylene and vinyl acetate copolymer.

[0013] In some embodiments, the present disclosure provides a hot melt adhesive of low application temperature for use in frozen packagings which are maintained at low temperatures. [0014] In some embodiments, the present disclosure provides a hot melt adhesive with low application temperature for use in packaging subjected to temperatures of up to about 9O⁰C, as it may occur during the transportation and storage of certain materials.

[0015] In some embodiments, the present provides a hot melt adhesive with low application temperature (120 to 14O⁰C) with the difference between its softening point and application temperature ranging between approximately 2O⁰C and approximately 3O⁰C.

DETAILED DESCRIPTION

[0016] This disclosure refers to a hot melt adhesive comprising a resin, a polyethylene oligomer of low molecular weight (also known as polyethylene wax) and an ethylene and vinyl acetate copolymer.

[0017] The importance of continuous development of hot melt adhesives with low application temperature which present properties of adhesion, cohesion and resistance to heat acceptable for use in the most varied markets is highlighted in U.S. Patent 6,794,443. One of the markets where there is a need to develop an adhesive with more suitable mechanical properties is the market of packaging for frozen products, considering that currently available hot melt adhesives used have high application temperatures( of about 150 to about 18O⁰C).

[0018] One reason why hot melt adhesives with low temperature of application are highly desired by the consumer is related to the use of lower application temperature when compared to hot melt adhesives with a high application temperature, consequently requiring less electric energy for their heating.

[0019] Another advantage of hot melt adhesives with low application temperature relates to the reduction in the frequency of maintenance of the hot glue gun appliers, since there is no carbonization or formation of crusts caused by the use of high temperatures.

[0020] Another important factor to be considered relates to the safety of the operator who handles the hot adhesive. The lower the application temperature of the adhesive, the lower the severity of burns that a possible spillage could cause an operator. [0021] By this way, as previously explained, several embodiments are described with the objective of combining the advantages of hot melt adhesives with low application temperatures with the performance properties of hot melt adhesives with high application temperatures. As an example, we can cite Patent Application US2006116459, which uses, among other raw materials, a wax with a softening point from about 51⁰C to about 83°C. The low softening point of the wax used confers a low softening point to the adhesive itself and this behavior is consistent with that observed in commercially available products.

[0022] The adhesives currently available in the market have a softening point between 70 and 85⁰C. Considering that the application temperature of said hot melt adhesives with low application temperature ranges between 120 and 14O⁰C (typically 13O⁰C), the commercially available adhesives have a difference between its softening point and application temperature of 50-65⁰C.

[0023] One disadvantage of the above-mentioned adhesives relates to the temperature reached during the transportation of the products (e.g. packagings). Depending on the place or the time of the year, transported or stored packages can reach high temperatures (up to 7O⁰C), resulting in the softening of the adhesive and subsequent opening of the packaging.

[0024] Another disadvantage concerns the open time of the adhesive. Open time is a property related to the time in which the adhesive can be processed or manipulated. This property is proportional to the proximity between the application temperature of the adhesive and its softening point. The closer a temperature is to another, the shorter is the open time because the adhesive solidifies faster. In the majority of the applications, the open time should be short since production lines are very fast, and it is necessary that the adhesive solidifies quickly, allowing the complete closure of the packaging. The open time, however, should not be so short as to damage the application of the adhesive due to excessively high viscosity or, in extreme cases, solidification of the adhesive before the joining of the parts to be adhered thereto. Thus, adhesives with high application temperature and low softening point take longer to solidify and effectively promote the adhesion between the substrates. This same behaviour is observed for adhesives with low application temperature, which also have low softening point. In production lines this delay in effectively closing the packaging can lead to undesired opening thereof.

[0025] A further disadvantage relates to the safety of the operator who handles the adhesive. The lower the melting point of the adhesive, the greater the probability of its spreading over the body of the operator in the case of accidental spillage of the product on the skin. This may be observed because the adhesive takes longer to solidify.

[0026] The hot melt adhesive according to some embodiments of this disclosure overcomes the above mentioned disadvantages due to the fact that: i. the adhesive has a softening point ranging between 100 and 115⁰C, and is consequently resistant to the high temperatures to which the substrates are subjected during transportation or storage. ii. the adhesive has an ideal balance of properties, especially related to the open time. It is short enough to guarantee that the adhesion between the substrates is efficient, whilst at the same time preventing the viscosity of the adhesive from increasing so quickly as to damage the handling and application thereof. iii. the adhesive of this disclosure is less likely to cause burns, since, on coming into contact with the skin of the operator, its cooling is practically instantaneous due to the negligible difference between the temperatures of application and softening.

[0027] As well as the above-mentioned advantages, in some embodiments, all the raw materials used are in accordance with the rules of the US FDA to section 175.105 - adhesives.

[0028] The adhesive of the disclosure has a relatively high softening point (when compared to conventional hot melt adhesives with low application temperatures), wherein the difference between the application temperature and the softening temperature of the adhesive ranges between approximately 2O⁰C and approximately 3O⁰C, in one embodiment being approximately 25⁰C. [0029] Thus, while the hot melt adhesives with low application temperature available in the market are formulated in such a way that the softening point ranges between approximately 7O⁰C and 85°C, which represents a difference of 50 to 65°C in the application temperature, the hot melt adhesive of this disclosure has a softening point ranging between 100 and 115°C, which means a difference of 20 to 30⁰C.

[0030] Two important factors were considered for the embodiment of the adhesive of this disclosure:

[0031] 1. Percentage of Vinyl Acetate (VA) present in the copolymer of EVA (Ethylene Vinyl Acetate). It is known that the greater the percentage of comonomer VA in the copolymer, the lower the crystallinity of the same, resulting thus, in greater flexibility. Adhesion is also influenced by the increase in the polarity of the polymer, a characteristic conferred by the presence/quantity of polar groups in the chain.

EVA copolymer

[0032] 2. Melt flow index (MFI) of the EVA: this index measures the fluidity of the material. The higher the index, the less viscose the polymer, and as a consequence, the hot melt adhesive which uses the polymer as raw material. For adhesives of this type it is necessary to have a suitable viscosity, that is to say, low viscosity to facilitate the application and exchange of heat with the environment, affecting the cooling of the material. The use of EVA copolymers with MFI equal or greater than 800g/10 min is especially desired for the adhesive of this disclosure, which comprises in total weight: i. 10-30% of a wax with softening point between 100⁰C and 12O⁰C, and whose function is to reduce the viscosity of the adhesive and regulate the open time;i. 25-45% of an EVA polymer, whose VA percentage is equal to or greater than 28% and is used to confer flexibility to the adhesive due to the size of the chain; iii. 40-60% of tackifying resin, which confers tactility and promotes the adhesion of the material.

[0033] The adhesive of this disclosure has the following properties: a) Softening point ranging between 100⁰C and 115⁰C. b) Application temperature: 120 - 14O⁰C.

[0034] Examples of tackifying resins used in the present disclosure are the colophony resins available in the market under the commercial name HAROSIN-X (commercialized by the company Harima do Brasil Ltda, Parana, Brasil) or Colofony WW/X (commercialzed by the company Resinas Brasil, Sao Paulo, Brasil).

[0035] Examples of ethylene and vinyl acetate copolymer-based polymeric resins used in this disclosure are the resins available in the market under the commercial name EVATANE 28-800, EVATANE 33-15, EVATANE 33-400, EVATANE 40-55, EVATANE 42-60 (commercialized by the company ARKEMA, Paris, France), available under the commercial name ELVAX (commercialized by the company E. I. du Pont de Nemours and Company, Delaware, United States), or available under the commercial name ESCORENE (commercialized by the company Exxon Mobil Corporation, Texas, United States).

[0036] Examples of waxes with a softening point between 100 and 120⁰C used in this disclosure are polyethylene waxes with low molecular weight, such as waxes available in the market under the commercial name MEGHWAX CPB 500 (Megh Indύstria e Comercio Ltda., Sao Paulo, Brazil). Another type of wax which can be used in this disclosure are hydrocarbonic waxes of basically linear and saturated chains, such as, for example, the waxes obtained by Fischer- Tropsch process, which are polymethylene waxes obtained from natural gas. These waxes are available in the market under the commercial name PARAFLINT H-I or PARAFLINT H-8 (commercialized by the company Sasol S. A, Johannesburg, South Africa) or BARECO PX- 105 Polymer (Baker Petrolite / Baker Hughes Incorporated, Texas, United States). In the case of the PARAFLINT H-I or PARAFLINT H-8 wax, the softening point thereof is approximately 108⁰C, and in the case of BARECO PX-105, its softening point is approximately HO⁰C. [0037] Examples of antioxidants are the materials commercialized under the commercial name Irganox 1010 (Ciba Specialty Chemicals, Basel, Switzerland).

[0038] In general the adhesive of this disclosure has a viscosity of 900-3000 mPa.s at a temperature of 13O⁰C.

[0039] The present disclosure is exemplified, but is not limited, by the examples below.

[0040] Examples

[0041] The embodiments herein described were prepared in accordance with the following process.

[0042] To a stainless steel vessel, the colophony resin was added and the temperature adjusted to 150⁰C. Using a mechanical stirrer, the resin was kept under agitation until the melting was complete, followed by the addition of the antioxidant charge as specified in the Example tables below. After the dissolution of the antioxidant, and still under agitation, the EVA copolymer was added. After melting of the EVA copolymer, the hydrocarbon wax was added to the vessel. The mixture was kept under agitation until complete homogenization and was subsequently extruded in the form of pellets.

[0043] The raw materials used in the examples below include:

1) Colophony resin with acidity between about 158 - 170 mg KOH/g, softening point between about 72 and about 8O⁰C and saponification index minimum of 164mg KOH/g;

2) EVA copolymer with vinyl acetate and melt flow index as specified in each example table;

[0044] Hydrocarbon wax with softening point between about 115 and about 12O⁰C. Example 1

Example 2

Example 3

Example 4

Example 7

Example 10

[0045] In general the adhesive of this disclosure has a viscosity of 900-3000 mPa.s at a temperature of 13O⁰C.

[0046] Properties

[0047] The viscosity of the adhesive was measured according to Standard ASTM D- 3236-88 ("Test Method for Apparent Viscosity of Hot Melt Adhesives and Coating Materials") and using a Brookfield Viscometer available as model RVT or RVDV-II+ (Brookfϊeld Engineering Technologies, Middleboro, Massachusetts) coupled with thermo- container.

[0048] The softening point was measured according to standard ASTM E 28-99 ("Softening Point of Resins Derived from Naval Stores by Ring-and-Ball Apparatus") and using a softening point equipment such as available under the trade designation R36 5 G (commercialized by PAC Petroleum Analyzer Company L. P, Houston, Texas).

[0049] It will be evident to any skilled in the art that this disclosure is not limited to prior illustrative examples and may be achieved in other specific forms, without abandoning its essential attributes. It is, therefore, desired that the examples be considered in all of their features, as illustrative and non-restrictive, reference being made to the attached claims and all the alterations which may be found within the meaning and scope of the equivalence of the claims, and thus intended to be included here.

Claims

What is claimed is:

1. A hot melt adhesive comprising a wax, an ethylene and vinyl acetate copolymer and a tackifying resin, wherein the wax has a softening point between 100⁰C and 12O⁰C.

2. The hot melt adhesive of claim 1 wherein said wax is a polyethylene wax with softening point between about HO⁰C and 12O⁰C.

3. The hot melt adhesive of claim 1 wherein said wax is a polyethylene wax obtained by Fischer-Tropsch process.

4. The hot melt adhesive of claim 1 wherein said ethylene and vinyl acetate copolymer has a percentage of vinyl acetate equal or superior to 28%.

5. The hot melt adhesive of with claim 4 wherein the ethylene and vinyl acetate copolymer has a melt flow index of at least 800g/10 min.

6. The hot melt adhesive of claim 1 wherein said adhesive has a softening point between 100⁰C and 115⁰C.

7. The hot melt adhesive of claim 1 wherein the adhesive has a viscosity of 900-3000 mPa.s at a temperature of 13O⁰C.

8. The hot melt adhesive, in accordance with any one of the preceding claims, wherein the adhesive comprises by weight: a. 10-30% of the wax with a softening point ranging between 100⁰C and 12O⁰C; b. 25-45% of the ethylene and vinyl acetate copolymer; c. 40-60% of tackifying resin.

9. The hot melt adhesive according to any one of claims 1 to 8, wherein said wax is a polyethylene wax of low molecular weight.