JPH0233739B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention generally relates to a vinylidene chloride copolymer resin film obtained by extrusion film formation and a method for producing the same. There are many types of protective packaging, such as wax paper,
Plastic coated paper, aluminum foil, and polyethylene film are used, but vinylidene chloride copolymer film is the most widely used because it has low permeability to water vapor and gas, and is resistant to mechanical and chemical deterioration. It is used. However, vinylidene chloride copolymer films often do not have sufficient tack or cohesiveness to self-adhere, so they do not adhere even under small pressures such as those used in domestic applications, and therefore They are often unsuitable for retaining flavor, moisture and other desired properties in fresh or processed food products. Therefore, in order to increase the tackiness of the film, various additives are often mixed into the vinylidene chloride copolymer composition to form a film. In the case of vinylidene chloride copolymer compositions for extrusion, as described above, the additives incorporated are often in liquid form (for example, citric acid esters are examples);
It is characterized by having the dual function of not only a plasticizer or extrusion aid but also a tackiness improver. While the aforementioned additives have been useful in imparting tack to vinylidene chloride copolymer compositions containing the additives, they have introduced new problems. For example, strong tack additives are usually incompatible with vinylidene chloride copolymer resins and can sometimes bleed onto the surface of the film and, in extreme cases, may cover the surface or come into contact with film making or film handling machinery. This causes abnormalities in operation and product quality. Furthermore, some of the additives are thermally unstable and extrusion compositions tend to decompose during thermal processing and smolder within the extruder, causing undesirable odors and colors in the product. Such severe color and odor can also be alleviated by incorporating antioxidants into the composition, but such antioxidants are very expensive and less desirable to film manufacturers. It's something that doesn't exist. Moreover, such additives, at the cost of providing high tack, necessarily unbalance other physical properties. High tack properties are necessary for films for industrial applications, and even with prior art additives, high tack can be achieved by increasing the amount added.
By increasing the tackiness, only a product with poor workability can be obtained. That is, the films stick together so strongly that they tear or destroy the film when they are separated (i.e., the "blocking" effect).
Either severe handling problems arise, or the film is easy to handle but has insufficient tack. In addition to the handling problems mentioned above, increasing the amount of additives can cause other detrimental properties such as decreased film modulus as well as increased oxygen and water vapor permeability and increased cost. There is a tendency. The present invention is a highly tacky film that has an inherent tackiness that allows it to form a seal by applying slight pressure, and that the seal can be pulled away without destroying the film. It is a low-blocking film that has no strong odor, color, high transparency, or high cost.
The objective is to provide a film in which the aforementioned problems of modulus reduction are not as pronounced as with conventional plasticizer-tack additives. Also, a method for producing a film that can make a relatively rigid film with high tackiness from a composition that is low in vinylidene chloride and vinyl chloride residual monomers, is easy to extrude, and is relatively inexpensive. It provides: The highly tacky thin film of the present invention is comprised of an extrudable vinylidene chloride copolymer resin and a copolymer grease (e.g., a copolymer of ethylene and vinyl acetate), and the grease copolymer at least improves tackiness. The grease copolymer is contained in an amount of 10% by weight or less to produce an improving effect, and the peak molecular weight of the grease copolymer is in the range of 500 to 7,500 as measured by gel permeation chromatography. The vinylidene chloride copolymers used in the practice of this invention are obtained by copolymerizing a major portion of vinylidene chloride monomer with at least one other comonomer and are formed into a film under extrusion conditions. Any copolymer that can form a product may be used. Typically, such extrudable vinylidene chloride copolymers are normally crystalline and contain 70-95% by weight vinylidene chloride, with the remainder being one or more ethylenically unsaturated comonomers, e.g. vinyl chloride. , vinyl acetate, vinyl propionate, acrylonitrile,
Alkyl and aralkyl salts of acrylic acid and methacrylic acid in which the alkyl and aralkyl groups have about 8 or less carbon atoms, acrylic acid, acrylamide, vinyl alkyl ether, vinyl alkyl ketone, acrolein, aryl ester, aryl ether, butadiene , chloroprene, etc. Typical three-component compositions used include:
Vinylidene chloride and e.g. acrolein and vinyl chloride; acrylic acid and acrylonitrile; alkyl acrylates and alkyl methacrylates; acrylonitrile and butadiene; acrylonitrile and itaconic acid; acrylonitrile and vinyl acetate, vinyl propionate or vinyl chloride; alkyl esters or ethers and chlorides Vinyl; polymers of butadiene and vinyl acetate, vinyl propionate or vinyl chloride; vinyl ether and vinyl chloride. Not only mixtures of vinylidene chloride, but also four or more component polymers of similar monomer compositions can be used advantageously. The vinylidene chloride copolymer can be made by any method suitable for producing extrusion resins of the copolymer, for example by suspending or emulsifying it in a mass or in an aqueous medium. There is polymerization by polymerization technology. Commonly used copolymer greases of ethylene and vinyl acetate contain 10 to 65% by weight, preferably 35 to 50% by weight of vinyl acetate, including partially hydrolyzed derivatives. Although small amounts of other copolymer monomers may also be included in the copolymer,
It is limited to a range that does not adversely affect the properties of the copolymer. Copolymers suitable for use as tack additives in the vinylidene chloride copolymer films of this invention are those that have typical characteristics as greases or oils. The molecular weight of such copolymers typically ranges from 500 to 7500, preferably from 1000 to 7500, as determined by gel permeation chromatography.
In the range of 4000. A gel permeation chromatography method for determining the molecular weight of polymers was published by JC Moore in J. Polymer Sci.A.
2835 (1964). Also, LH
J. Appl. Polymer Sci., 10345 (1966) by Tung.
and J.Appl.Polymer Sci. by WNSmith,
11639 (1967). The melt flow rate of the copolymer exceeds the range that can be accurately measured using ASTMD-1238-70(E) at 190°C and 2.16 kg, so in order to obtain a more meaningful value, we Some of the conditions of the test method need to be changed. Diameter of plasticity meter orifice
Reduced to 0.0200±0.0002 inch and test temperature 80℃
Using the equipment and procedure of ASTMD-1238-70(E) except that the copolymer used in the present invention was
50, preferably 10-25 decigram/minute (dg/
(min) range of melt flow rates. Copolymer greases of low molecular weight are made by polymerizing the corresponding monomers at high temperatures and pressures in the presence of free radical catalysts. Although the preparation of grease copolymers is not part of this invention, a suitable method of preparation is described in U.S. Pat. No. 2,395,381, except for the use of high temperatures and high concentrations of catalyst. In a preferred method, up to about 20 weight percent of a telomer, such as ethylene or propylene, based on the total weight of comonomers, is added to the polymerization zone to suppress the formation of high molecular weight copolymers. The amount of grease copolymer added to vinylidene chloride copolymer for extrusion depends on the degree of tackiness required for the film product, but in general, the proportion of grease copolymer added to the vinylidene chloride copolymer for extrusion is determined from the amount that produces the effect of improving tackiness. It accounts for up to 10% by weight of the composition, preferably from 0.1 to 7%. The actual amount required to achieve the desired tack will vary depending on the molecular weight of the copolymer grease and the proportion of ester comonomer in the copolymer. Conventional additives such as heat stabilizers and the like may be included in the extrusion composition if needed or desired.
Although antioxidants, such as those used in conventional tack additives, have not been found necessary for the copolymer greases used in this invention, small amounts of such materials can be used if desired. It's okay. However, traditional high-viscosity tack additives should be avoided, as they can leach onto the surface of the film and reveal the tack-enhancing effects of the copolymer. Mixing of the copolymer grease and other additives, if any, with the vinylidene chloride copolymer for extrusion can be carried out using conventional resin mixing methods and equipment, such as a homogenizing blender or a mixing extruder.
Since the low molecular weight copolymer additive takes part in improving the adhesion efficiency, it is advantageous to mix all components as thoroughly as possible. Because the copolymer grease additive is viscous, it is particularly advantageous to heat the low molecular weight copolymer slightly before mixing with the vinylidene chloride copolymer for thorough mixing. Although the most advantageous and convenient method of achieving thorough mixing is to add the copolymer grease to the polymerization reactor along with the monomers used to make the vinylidene chloride copolymer, If a reactor is used, care should be taken not to add the copolymer grease after the monomer dispersion has formed, as this will result in the formation of copolymer grease on the surface of the aqueous medium. This is because the layer will interfere with the addition of the polymerization terminator after it is formed. Such methods are frequently used in this field. The mixture of vinylidene chloride copolymer and low molecular weight copolymer grease is made by any of the above-mentioned variations and then processed by conventional methods known for making films from vinylidene chloride copolymer, viz. The melt-extruded parison is formed into a film by a film forming method called a cast film method or an inlay film method to form a stretched or unstretched thin film. Films made in accordance with the present invention typically have a thickness of about 0.2 mil (0.0051 mm) to about 1.5 mil.
(0.038mm), preferably 0.4mil (0.0102mm) to 1mil
(0.0254 mm), although thicker films or sheets can be made if desired. In the present invention, both are collectively referred to as a film. The examples in the following table illustrate the characteristics of films formed by the manufacturing method of the present invention and should not be construed as limiting the scope of the claims. In the examples, parts and percentages are by weight unless otherwise indicated or required by context. Adhesion testing of the film was conducted by a method consisting of making one section of film and another section measuring 5 inches by 8 inches. The first section is then secured vertically to the top surface of the metal plate at an angle of 30° from the horizontal, by taping the edges and clamped onto the top load scale. Then place another section of film over the first section, face-to-face, and tape the top edge of the other section, leaving the bottom edge untouched. It is necessary to overlap the two parts so that there are no wrinkles, folds or bubbles.
Then attach a fastener to the bottom free end of the other section, attach it to a wire hook, and attach it to the bottom of a mobile cart. The wheel is raised by means of pulleys and motors and travels on an inclined track, the free end of the other part of the film being continuously pulled vertically upwards from the first part, thereby Peel or separate the two parts of the film and allow the peeled sides to spread at a constant rate of 5 inches per minute. Then the average force (g) required to separate the two parts
Read from the scale. Blocks are long-term tack in nature, and the method used to measure tack is that after carefully removing two complete overlapping film sections from a roll of film that is over a week old, the method used to measure tack is similar to that of film sections. Measure the force required to separate. In-monomer addition of ethylene-vinyl acetate copolymer grease to the same vinylidene chloride copolymer as in the prior art practice of mixing Citroflex A-4 plasticizer with vinylidene chloride copolymer. Tests were conducted to compare the physical properties of the blocks, including stiffness (measured with a 2% Secant modulus), block and adhesion (measured with a 30-day Mettler Tester).

【table】

[Table] As shown in Table 1, stiffness can be increased by using a copolymer grease instead of a plasticizer. When using copolymer greases, the tack in grams is greater when measured after 27/30 days.
Limited oxygen permeation data showed little change. Highly tacky, high stiffness films are particularly advantageous as household films because they are tangle-resistant, tear easily from rolls, and have good adhesion for sealing applications. The copolymer grease mixes well, acts as an extrusion aid, and does not require operating conditions that would cause degradation (color) of the vinylidene chloride copolymer resin. It has been found that the amount of residual vinyl chloride and vinylidene chloride monomers is reduced by using in-monomer addition of copolymer greases compared to conventional plasticized resins. Table 2 below shows the residual monomer data obtained. Experiment number
4955 is a case where a conventional plasticized vinylidene chloride copolymer resin was used, and the other experiments were conducted using the same vinylidene chloride copolymer resin, but instead of a plasticizer, simply in-monomer of the copolymer grease of the present invention was used.
monomer) is used.

Table: The copolymer greases used in the present invention are highly viscous and usually sticky materials that are difficult to handle and clean. Although proper handling and transportation must be considered, there are many advantages to using this relatively inexpensive material that outweigh some handling inconveniences. Although several exemplary embodiments and details have been shown to illustrate the invention, it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the spirit of the invention and the scope of the claims. Will.

Claims (1)

[Claims] 1. A highly adhesive film obtained by extruding and forming a vinylidene chloride resin into a film, with a molecular weight value (peak value) determined by gel permeation chromatography in the range of 500 to 7500. The grease is made of a vinylidene chloride copolymer containing 10% by weight or less of copolymer grease of ethylene and vinyl acetate located in An extruded vinylidene chloride resin film characterized by a stiffness value of 90,000 Psi or more measured by a second modulus test method. 2. Before copolymerizing vinylidene chloride resin, gel
Copolymer grease of ethylene and vinyl acetate whose molecular weight value (peak value) determined by permeation chromatography is in the range of 500 to 7500 is added in a proportion of 10% by weight or less. death,
A vinylidene chloride resin copolymer was obtained in the presence of the copolymer grease, and the resin copolymer was melt-extruded to form a film, and the adhesive value measured by the Mettler test method was 5 grams or less and 2% A method for producing a vinylidene chloride resin film, characterized by obtaining a film having a stiffness value of 90,000 Psi or more as measured by a second modulus test method.