JPH0446308B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to adhesive compositions, film laminates, and pouches or tubes for retort foods or products made therefrom.

Certain packaging applications, such as retort packaging, require that the packaging material constitute a good barrier to the passage of oxygen and moisture vapors. Furthermore, some food packaging requires that a minimum amount of oxygen or air be permeated to the contents. Cheese is one food product that should be packaged to exclude oxygen.

Stretched polyacrylonitrile (PAN) film has excellent oxygen barrier properties. However, its moisture barrier properties are worse than desired for retort packaging. Moreover, it is not itself heat sealable. Both deficiencies can be overcome by applying a layer of thermoplastic material with good moisture barrier properties to the PAN surface. However, due to the significant chemical dissimilarity between PAN and thermoplastic moisture barrier polymers such as polyolefins, adhesion between both materials is poor and packaging integrity is problematic. It is therefore necessary to consider inserting an adhesive system or bonding system between the PAN and the thermoplastic moisture barrier, which will act as an interadhesive bridge between both these materials. However, it has been discovered that materials that exhibit good adhesion to PAN generally do not exhibit good adhesion to other polymeric materials such as polyolefin films.

Previous practice of providing an adhesive bridge between a PAN and an effective moisture barrier film has involved the application of an adhesive such as polyurethane or polyester in a liquid vehicle. By this means, the adhesive
It is applied to the PAN and then the moisture barrier film is laminated to the PAN via this adhesive. Such methods, despite the use of expensive adhesives of this type, have not provided the industry with flexible film laminates that are economical and effective for retort food pouch applications.

In recent years, the food packaging industry has shown strong interest in the concept of pouch-packaged foods, which eliminate the need for refrigeration for preservation and therefore avoid costly and energy-intensive frozen transport, among other advantages. and storage facilities can be omitted. Flexible retorts using materials that are toxicologically safe as well as able to withstand the rigors of disinfection and subsequent reheating and provide a barrier that is sufficient to adequately protect the contents during storage. Significant efforts have been made to develop food pouches or pressure cooker food pouches.

According to U.S. Patent No. 3,453,173, a polyolefin-polyacrylonitrile laminate, which is said to have excellent heat-sealing strength and excellent barrier properties against gas permeation, and is suitable for food container construction, is capable of bonding a polyolefin surface with a polyacrylonitrile material through a single adhesive. It is created by crosslinking acrylonitrile surfaces together and adhering their adjacent surfaces. In order to make one or both of these surfaces more adhesive, they may be treated, for example, with a gaseous mixture of boron trifluoride, as described in British Patent No. 834,196, or as described in US Pat. No. 2,632,921. Preheating can be achieved in a certain way by treatment with corona discharge. Among the adhesives used to make the laminates are the ethylene-vinyl acetate copolymers described in US Pat. No. 2,200,429. Interlayer adhesion in boiling water is not expected to be strong because the manufacturing conditions and intended adhesive do not contribute to primary valence bonds.

In order to use the metal layer as an effective surface, measures have also been taken to metal plate the PAN film and bond it to the water vapor barrier film through this metal layer. This is also a somewhat expensive compromise.

One object of the present invention is to provide a new and effective adhesive composition that has particular utility in bonding together surfaces, particularly organic film surfaces.

Another object of the invention is to provide a film laminate using this adhesive composition of the invention.

Yet another object of the present invention is to provide a product or food pouch or tube that is effective in withstanding the rigors of hot or boiling water.

In accordance with the present invention, there is provided an adhesive composition for use in bonding together polymeric surfaces, the adhesive comprising: (a) a styrene-butadiene weight ratio of 1 to 3:3 to 1; (b) a resin in which the weight ratio of cyclopentadiene to styrene is from 1:2 to 1:4; and (c) (1) 1,3-pentadiene, (2) monocyclic terpene, and (3) A random terpolymer of alpha-methylstyrene consisting of a homogeneous combination of these monomers in a weight ratio of 3 to 4:3 to 4:2.5 to 3.5, respectively; 10(a), 0.5
(b) of 1.5 to 1.5 and (c) of 2 to 4.

According to the invention, among other uses,
Flexible film laminates suitable for use in the manufacture of product pouches or tubes or other articles for food packaging are provided, the laminates being bonded together by the adhesive composition of the present invention. Consists of two or more than two polymer films.

Further in accordance with the present invention there is provided a product pouch or tube made from any of the laminates described herein.

As noted above, the adhesive composition of the present invention is a combination of the three materials broadly mentioned above. The first material of this combination, a styrene-butadiene block copolymer, is commercially available, for example, as the Kraton 1000 series product (Siel Chemical Company, Polymer Division). One substance, Kraton 1102, is approximately 28
It is a styrene-butadiene block copolymer containing % styrene and about 72% 1,4-butadiene by weight, and has a molecular weight between 75,000 and 150,000.

The second substance of the adhesive composition as defined above has a weight ratio of cyclopentadiene to styrene of 1:2 to 1:
4, a cyclopentadiene-styrene resin. Its molecular weight ranges from about 350 to about 2500 and its specific gravity ranges from 1 to 1.3. This material is also commercially available. For example, Nebiyu LX685−180
A product known as is available from Nebiyu Chemical Company. This material is characterized by a softening point (ASTM E28 58T) of 302〓, a molecular weight of approximately 890, a specific gravity of 1.095, and this resin contains 89.9% carbon, 9.1
% hydrogen, the rest being oxygen and sulfur.

The third substance of the adhesive composition as defined above is 30 to 40
It is a random terpolymer of parts by weight of 1,3-pentadiene, 30 to 40 parts by weight of monocyclic terpene, and 25 to 35 parts by weight of alpha-methylstyrene. Although the preferred monocyclic terpene for use in the present random terpolymer is betaphellandrene, other monocyclic terpenes or mixtures thereof may be used. These include dipentene, alpha terpinene, beta terpinene, alpha elandrene, gamma terpinene, terpinolene, sylvestrene, origanene, pyronene, and the like.

Preferably, the terpolymer additive exhibits the following properties: melting point range (ring and ball), 75-125°C; specific gravity,
1.08−0.90; Bromine number, 614; Iodine number, 79; Acid number,
1 or less; saponification value, 1 or less; decomposition temperature (in air),
300°C; color (as a 50% toluene solution), Gardner 6; and viscosity (in toluene), 70%.

A particularly preferred random terpolymer is 37.5
By polymerizing a feed stream containing weight percent 1,3-pentadiene, 37.5 weight percent beta-phellandrene, and 25 weight percent alpha-methylstyrene in the presence of an aluminum chloride catalyst in a toluene diluent. able to make. The resulting terpolymer contains 34.0 parts by weight of 1,3-pentadiene, 36.5 parts by weight
Contains parts by weight of beta-phellandrene and 29.5 parts by weight of alpha-methylstyrene. This substance has a molecular weight (average weight) of 1880, a bromine number of 14, and a bromine number of 79
It has an iodine number of , a glass transition temperature of 38°C, a toluene viscosity of f to g of 70°C, and a decomposition temperature (in air) of 300°C.

When formulating the adhesive composition of the present invention, the preferred weight part ratios of the various components are as follows: 7-
10 parts by weight of styrene-butadiene block copolymer, 0.5-1.5 parts by weight of cyclopentadiene-styrene resin, and 2-4 parts by weight of random terpolymer.

The manner in which the three materials are kneaded together is not critical and does not form part of the invention. Preferably, these three components are physically mixed by any mechanical mixing device conventionally used to mix viscous adhesives or plastics, such as an extruder, Banbury mixer or differential roll mill. do. To aid thorough mixing of the polymers and develop the desired improved combination of physical properties, this mechanical kneading is carried out at a high enough temperature to soften the polymers so that they are completely dispersed and intermixed. do. Alternatively, these components may be solution mixed by dissolving the polymer in a solvent such as toluene. The adhesive can be applied from this solution to any surface desired to be adhesively bonded to another surface. It should be understood that the adhesive mixture of the present invention may also contain other additives for plasticizing, lubricating, dyeing, coloring, antioxidant, flame retardant, etc. the resin adhesive mix. .

Among the advantages obtained with the adhesive formulation of the present invention is its remarkable resistance to weakening or failure of its adhesive strength upon exposure to boiling water. The adhesive of the present invention finds exceptional utility in laminated bonding of organic films together. These films may be individual films of the same type bonded together, or may be laminated with different polymers to take advantage of the unique properties of each film. Preferred organic polymer films include polyacrylonitrile films and polyolefin films. However, as mentioned above, the present invention is not limited to laminating these two types of films.

Possible PAN films include homopolymer polyacrylonitrile. This film has an oxygen permeability of less than about 10 c.c./100 square inches/24 hours/atmosphere at 100 °C (38°C), more preferably less than about 0.1 cc/100 square inches/24 hours/atmosphere at 23°C. , and preferably 100〓
(38°C) and 90% relative humidity for less than about 50 g/100 square inches/24 hours, more preferably 100〓(38
It should have a water vapor transmission rate of less than about 10 g/100 square inches/24 hours at 100°C.

The oxygen and water vapor transmission rates mentioned above can be measured by various methods known in the art. For example, oxygen permeability can be conveniently measured with a Dollman Polymeric Permeation Analyzer, PPA-1 (Dollman Envirotech Corporation, Mountain View CA). Dow cells can also be used for this purpose according to ASTM D-1434. Preferably, a biaxially oriented film of acrylonitrile homopolymer made by the polymerization and film forming method described in US Pat. No. 4,066,731 is used.

Polyolefins useful herein include one or more alpha olefins, e.g.
Ethylene, propylene, butene-1, pentene-
1, hexene-1, heptene-1, octene-
1, etc., including film-forming homopolymers and copolymers formed by the polymerization of 1, etc. Useful polyolefins can also be copolymerized with one or more of the alpha-olefins up to about 20% by weight of the total, preferably up to about 5% by weight of the total alpha-olefin. Contains film-forming copolymers copolymerized with many monomers. These monomers include carbon monoxide, sulfur dioxide, acrylic acid, or acrylic esters such as methyl acrylate, amyl acrylate, hexyl acrylate, cyclohexyl acrylate, and the like. Additionally, alpha-olefins may include methacrylic acid or methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, amyl methacrylate,
It can be copolymerized with etc. They may also be copolymerized with vinyl acetic acid or vinyl esters such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, isopropylacetate, and the like.

Polyolefin films contemplated herein include mixtures and blends of polyolefins and one or more other polymers compatible therewith. Thus, for example, a polyolef-in-film may contain about 80% polypropylene and about 20% by weight polypropylene.
It can be made from a kneaded product of polyethylene. Polymers are also used here as processing aids, plasticizers,
Other ingredients such as antioxidants, reinforcing agents, fillers, pigments, etc. can be included in conventional amounts.

Although the adhesive composition of the present invention can be applied to the desired surface in a variety of ways, a particularly convenient way is to apply the composition from a dispersion or solution in a suitable organic solvent such as toluene. . After application of this solution or dispersion, the solvent is removed by drying and a pressure-sensitive adhesive film is obtained. The surface to be contacted with the adhesive can be compressed into intimate contact with the adhesive coating. Obviously both front surfaces may be coated with a thin layer of adhesive.

The individual films that make up the laminate in question here vary in thickness, approximately 0.1 mil (0.0025 mm)
mm) to about 10 mils (0.25 mm), preferably about 0.5 mils (0.0125 mm) to about 5 mils (0.125 mm). These films are assembled into a laminate using any one or more of several conventional methods, such as those described in U.S. Pat. No. 3,453,173, which is incorporated herein by reference. be able to.

The laminate of the present invention can be processed into a retort food pouch or tube using known methods. According to one such method, two superimposed layers of the laminate, with mutually facing heat heelable olefin surfaces, can be edge sealed between hot plates. The pouch or tube can then be filled with food and heat sealed on either or both ends to complete the packaging.

Example 1 An adhesive within the scope of the invention was made as follows: 30.8 g of a styrene-butadiene block copolymer (sold as Kraton 1101) containing 28% by weight styrene and 72% by weight 1,4-butadiene. .
Ciel Chemical Company, Polymer Division); 3.6 g of a cyclopentadiene-styrene resin having approximately 33% cyclopentadiene and approximately 66% styrene by weight (available as Neville LX685-180 from Neville Chemical Company); and 34
10.6 g of a random terpolymer of parts by weight of 1,3-pentadiene, 36.5 parts by weight of beta-phellandrene, and 29.5 parts by weight of alpha-methylstyrene (available as Super Star Tactic 100 from Reichhold Chemical Company).
was dissolved in 255 ml of toluene.

Example 2 A 7 x 12 inch (17.8 x 30.5 cm) piece of biaxially oriented polyacrylonitrile homopolymer film made according to the method disclosed in U.S. Pat. Apply with adhesive solution and remove the solvent by drying at 110°C for 5 minutes. This coated polyacrylonitrile film was heated to 270° (132°C) with a 3 mil (0.075 mm) polypropylene film.
and laminated in a flat plate press.

Half of this sample was exposed to boiling water for 30 minutes. Both boiled and non-boiled samples were tested for peel strength. Both samples weighed 1.5 lb/in (0.26
Kg/cm), indicating that the adhesion was not affected by boiling water.

The adhesive of the present invention is highly resistant to boiling water and can be used as a pressure sensitive adhesive for various polymers in addition to those listed above.

Claims (1)

[Scope of Claims] 1. An adhesive composition comprising: (a) a block copolymer having a styrene-butadiene weight ratio of 1 to 3:3 to 1; (b) a cyclopentadiene-styrene weight ratio of 1: 2 to 1:4; and (c) a random terpolymer of (1) 1,3-pentadiene, (2) monocyclic terpene, and (3) alpha-methylstyrene, the weight ratio of these monomers is 3 to 4:3 to 4:2.5 to 3.5, respectively; consisting of a homogeneous combination of (c) An adhesive composition. 2. The adhesive according to claim 1, wherein the monocyclic terpene is beta-phellandrene. 3. The adhesive according to claim 1, dissolved or dispersed in an organic medium. 4 (a) each have a styrene-butadiene weight ratio of 1:2.5; (b) each have a cyclopentadiene-styrene weight ratio of 1:2; (c) each have a 3.5:3.5:3 (1) The adhesive according to claim 1, having a weight ratio of :(2):(3). 5. An adhesive according to claim 4, wherein the combination consists of 8 parts by weight of (a), 1 part by weight of (b) and 3 parts by weight of (c).