JPS5993324A - Aging method of polyvinylidene chloride resin coat film - Google Patents

Abstract

PURPOSE:To crystallize PVDC, by applying polyvinylidene chloride resin (PVDC) on a base material film, drying the resin, winding the film, forming a temprature gradient with the core of said wound film being at a high temperature and with the surface layer being at a low temperature, thereby preventing a brushing phenomenon, and performing aging. CONSTITUTION:PVDC is made to be solvent solution, aqueous latex, or the like and applied to a base material film (e.g., polyamide film or the like) and dried, and coat film is obtained. Then, said coat film is wound around a core and the like, wherein a heater is built in. The core of the winding is made to be a high temperature and the surface layer is made to be a low temperature. Thus a temperature gradient is formed. Under the wound state, aging is performed, and the PVDC is crystallized. Furthermore, it is recommended that the temperature of the winding core should be controlled according to a temperature increasing program. EFFECT:Oxygen gas barrier property and the bonding power of a coat layer are not impaired and productivity is improved. USE:Wrapping material for food.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for aging a polyvinylidene chloride resin (hereinafter referred to as PvDC) coated film, and its purpose is to deteriorate the oxygen gas barrier property and the adhesive strength of the coated layer. The purpose of the present invention is to efficiently produce a PVDC coated film that does not cause any brushing phenomenon.

Biaxially stretched films such as polyamide, polyester, and polypropylene have excellent strength, transparency, and one-dimensional stability, and are widely used as packaging materials.

Particularly when high oxygen gas barrier properties are required in the food packaging field, a PVDC coating is further applied to one or both sides of these base films.

In this case, a PVDC solvent solution or PVDC aqueous latex is coated on a base film using a coating device such as a gravure coater or an air knife coater, dried in an arch-type or 70-ring type drying oven, and then wound up. The performance of the layer as it is is not sufficient and further aging treatment is usually required to crystallize the PVDC. In particular, when PVDC water-based latex, which is advantageous in terms of raw material costs and equipment costs, is selected as a coating liquid, aging treatment is essential, and this treatment provides excellent oxygen gas barrier properties.

Furthermore, a film without clouding of the coating layer can be obtained by retorting or using a solvent.

The ideal PVDC coating method uses a latex with excellent coating suitability and operability such as emulsion pot life, and oxygen gas barrier properties.

In order to manufacture a coated film that satisfies all of the performance requirements such as the adhesive strength between the base film and the coating layer, the adhesive strength between the printing ink and the laminate film, and the optical uniformity of the coated film, aging treatment is performed using conventional methods. That is, this is difficult to achieve when the roll is left in a high-temperature atmosphere.

Coated layer with highly crystalline PVDC emulsion.

If the PVDC is hardened by crystallization to some extent during drying and then rolled up, the brushing phenomenon will not occur.9 For example, from the viewpoint of the pot life and adhesiveness of emulsion, it is difficult to use PVDC that is too crystalline, and therefore, PVC IJ is difficult to use. A PVDC latex in which the type and amount of the copolymerized component relative to the polymer are controlled to slow down the crystallization rate to some extent is advantageous in terms of operation. A particularly important operation for the film obtained by applying and drying this type of latex is aging treatment to increase the degree of crystallinity and improve the oxygen gas barrier properties. However, due to this, aging treatments according to the prior art often result in a brushing phenomenon that impairs the optical uniformity of the product film.

In addition, the adhesive strength between the base film and the coating layer and the lamination adhesive strength between the coating layer and a sealant film such as polyethylene are important factors that determine the strength of the laminated packaging material, so these performances cannot be ignored. Adhesive strength and brushing phenomenon are often in a contradictory relationship, and films coated with PVDC latex, which has good adhesive strength, tend to suffer from brushing phenomenon due to aging treatment,9 making it difficult to achieve both performances at the same time.

Brushing here refers to mild blocking, which is thought to occur through a 9-order mechanism.

That is, in many cases, it is necessary to age coated and dried PvDC at a certain temperature in order to efficiently and effectively increase the crystallinity.
Since the crystallization rate of is generally slow, it becomes a softened state before crystallization.

However, since the aging treatment is generally carried out in the form of a roll, the coating layer is the uncoated surface of the base film.

Or, in the case of double-sided coating, it is in contact with another coating layer. The coating layer, which has been heated to the aging temperature and softened, slightly adheres to the contact surface at some point during the aging period.
Part of the surface layer of the coating layer thins and transfers to the other side, and as a result, the surface of the coating layer that has crystallized after aging becomes partially rough, and the optical uniformity of the coating film is lost. .

Generally, brushing occurs more prominently on the core side of the film roll. This means that the base film exhibits rheological behavior that tends to return to its original state over time.

This is due to thermal shrinkage behavior, especially when heated.

5- In the conventional method of aging a film roll by leaving it in a high-temperature atmosphere, the surface layer of the roll is heated, so the outer layer shrinks first, resulting in a so-called tightened state.1
Excessive and uneven contact pressure is generated on the film on the core side. When the temperature of the core-side film in this state rises and the coating layer softens, a brushing phenomenon easily occurs.

The inventors of the present invention have conducted extensive research to solve the problems of the prior art, and as a result have arrived at the present invention.

In other words, the present inventors have developed a method of aging a PVDC coated film in the form of a roll by forming a temperature gradient in the radial direction of the roll, with the core side of the nine rolls being high temperature and the surface layer side being low temperature. It has been found that the PVDC coating layer of the core side Fill

By applying the method of the present invention, operability during coated film production, performance of the product coated film, i.e., oxygen gas barrier properties, adhesive strength between the base film and the coated layer, retort resistance of the coated layer, and solvent resistance are improved. It is possible to obtain a PVDC coated film that satisfies the above requirements at a high level and is free from optical non-uniformity caused by brushing.

The base film to which the present invention is applied includes nylon 6,
Polyamide films made of nylon 66 etc. or copolymers and mixtures containing these components, polyester films typified by polyethylene terephthalate,
Polyolefin films containing polyethylene and polyprohylene, polyvinyl chloride, polyacrylonitrile, polycarbonate, ethylene-vinyl acetate copolymers, polyvinyl alcohol, and mixtures thereof, films made from copolymers, and cellulose typified by cellophane. These films are usually biaxially stretched films, but may be uniaxially stretched films or unstretched films. These films may also contain additives such as lubricants, plasticizers, and antistatic agents.

The PVDC used in the present invention is almost never a homopolymer of polyvinylidene chloride;9 it is usually a copolymer of vinyl chloride, acrylonitrile, acrylic ester, etc. within the range that does not change the basic performance of polyvinylidene chloride. These PvDCs are coated onto a substrate film as a solvent solution or aqueous latex. Note that the method of the present invention is particularly effective when the coating liquid is aqueous latex.

For PvDC coating, PVDC is coated on one or both sides of a base film using an air knife method, gravure roll method, reverse roll method, barcode method, etc., and then a solvent is applied in an arch type or floating type drying oven.

The most common method is to remove water, but if the base film is a biaxially stretched film, there are methods such as coating before biaxial stretching, coating after longitudinal stretching, and then laterally stretching the film, etc. The method of the present invention can also be applied.

Next, the method of the present invention can be carried out, for example, by the following means.

(1) The coated film is wound around a metal core with a built-in heater or a laminated core made of metal and resin and paper.

The surface and edges of the roll are coated with asbestos, 1 Styrofoam, etc. Insulate with heat insulating material to control core temperature.

(2) A coated film is wound around a core made of paper, resin, or metal, and heated with hot air, infrared rays, etc. from the hollow part of the core.

In this case, the surface and end surfaces of one roll may be kept warm, or the temperature may be actively controlled using another heat source or coolant.

According to the research of the present inventors, (1) is better,
In particular, the temperature of the metal core can be programmed to be controlled, for example at a low temperature in the early stages of aging (the heater is turned on over time).
It is even more effective to turn off the heater to delay the temperature rise in the area far from the heater. ) and increase the temperature of the core as the crystallized region on the 1st core side expands (also in this case, intermittent heating that repeats low and high temperatures is good), and uses the crystallized region as a heat transfer medium. It has been found that by adopting a method of controlling the temperature of the outer non-crystallized region, it is possible to perform the aging treatment in a short time without causing brushing, and the method of the present invention can be carried out most effectively.

In this case, the core temperature increase program is based on the thermal shrinkage behavior of the base film (shrinkage rate and shrinkage stress), the physical properties of PVDC (crystallization rate, softening temperature, adhesion), and the thickness of the base film and coating layer. , slip property needs to be determined experimentally depending on the length of one roll and the like.

If the base film is coated with PVDC, which has a large thermal shrinkage and is prone to brushing, and the diameter of the roll is large, it is necessary to set a mild temperature increase program.

Recent market demands for PVDC coated films for packaging are becoming increasingly strict, requiring high oxygen gas barrier properties as well as strict optical uniformity capable of producing subtle neutral color printing. It has been difficult to meet these demands with conventional aging techniques, but the method of the present invention, which was created as a result of a detailed study of aging methods that were conventionally considered relatively easy and roughly managed, can meet these requirements. It solves problems and has great industrial value.

The method of the present invention will be specifically explained below using Examples.

10- Example 1 One side of a nylon biaxially stretched film with a thickness of 15 μm was coated with a PVDC water-based latex containing 92% by weight of vinylidene chloride using an air knife method, and then dried in an arch drying oven to an outer diameter of 150 μm. It was wound around a stainless steel core with a built-in heater and thermometer. The thickness of the coating layer is 3μ
The winding length is 6050 m. After insulating the outer periphery and end of the scroll with heat insulating material, the aging process was performed by controlling the temperature of the stainless steel core using a human heating program. Note that the temperature of the roll at the start was about 25°C.

Processing time (hr) Temperature (°C) 40 30 45 35 6 5040 6 60 50 75 In other words, the aging treatment was performed for a total processing time of 34 hours, and then after cooling in the open for about 5 hours, the product was rolled back into a general-purpose paper tube. Finished. The oxygen gas permeation rate of the obtained film was 8 cc/yn''24 hr (20° C., 100% RH), and the film had excellent optical uniformity with no brushing observed at all.

Comparative Example 1 PVDC coating was performed under the same conditions as in Example 1, and the product was wound up into a 3-inch general-purpose paper tube. When the obtained roll was left in an atmosphere of 400 °C for 3 days to perform an aging treatment, brushing occurred on the 1000 m side of the core side of the film, and the degree of brushing was particularly severe on the 200 m side on the core side.

Patent applicant: Unitika Co., Ltd. 19-

Claims (1)

[Claims] 1. Polyvinyl chloride IJ on at least one side of the base film
After applying Den-based resin, drying and winding. A method of crystallizing polyvinylidene chloride resin by aging it in a rolled form, which is characterized by forming a temperature gradient in the radial direction of the roll, with the core side of the roll having a high temperature and the surface layer side having a low temperature. Aging method for coated film. 2. The aging method according to claim 1, wherein the temperature of the winding core is increased over time according to a preset temperature increase program.