JP2764212B2 - Heat sealable coating for styrene resin bonding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention forms a thermoplastic resin layer exhibiting good heat sealing property with respect to a styrene resin by being applied to a base material such as a plastic film or a metal foil. More specifically, a heat-sealing coating capable of forming a heat-sealing resin layer having a high heat-sealing strength by coating an aluminum foil as a cover material for a styrene-based resin packaging container. The agent is provided.

(Prior Art) Conventionally, it has been widely practiced to seal a lid material of a plastic container by using a sealing hot plate (heat seal bar), high frequency wave, ultrasonic wave or the like. The general form of the lid material is a metal foil typified by aluminum foil, paper or a heat-resistant plastic film, or a metal or a metal-deposited paper or film made of such a base material. Is provided with a heat-sealing resin layer having as a basic component. Further, in order to improve the heat sealing property, various variations such as providing a polyethylene resin layer as a buffer layer between the heat sealing resin layer and the base material have been performed.
On the other side, characters and designs are generally printed, and for protection, a heat-resistant transparent resin varnish is applied or a heat-resistant plastic film is laminated.

(Problems to be Solved by the Invention) Among plastics, so-called seal packs, which use a container mainly composed of styrene resin and seal the opening with a lid material, are widely used in various fields, mainly in the food packaging field. As the lid material, those obtained by applying a heat-sealing adhesive to aluminum foil are often used.

Various resin-based materials have been studied as a main component of a coating material for forming a heat-sealing resin layer of a lid material for a styrene-based resin container. It is evaluated as having good heat sealing properties.

However, the heat sealing strength is not always sufficient,
The reality is that improvements are required.

(Means for Solving the Problems) As a result of studying various resin systems and their blend systems, the present inventors have found that the heat-sealing resin layer of the lid material for a styrene-based resin container, which is the object of the present invention, has been developed. As a main component of the coating agent for forming, it was found that an acrylic resin-based material was good as conventionally recognized. In some cases, the heat sealing strength was slightly improved by known means such as blending an acrylic resin with another resin or adding an adhesion promoter.
However, when the heat sealing strength is improved, the heat sealing resin layer of the lid material tends to undergo cohesive failure when the heat sealing resin is peeled off from the styrene resin container, and the broken resin layer contaminates the contents. In addition, fragments of the resin layer adhering to and remaining on the edge of the container, which is called a so-called edge residue, cause discomfort when the container is used as tableware, which poses a practical problem.

The present inventors have solved the above-mentioned problems and have found that the heat sealing strength of the lid material for the styrene resin container is sufficiently large, and furthermore, when the lid is peeled off, the heat sealing resin layer is not broken without heat sealing. To obtain a heat-sealing coating material that forms a heat-sealing resin layer that can be peeled off at the interface between the heat-sealing resin layer and the container or at the interface between the heat-sealing resin layer and the aluminum foil as the base material of the lid material As a result, the non-volatile content of the acrylic resin solution of the heat-sealing coating agent containing the acrylic resin solution as a main component.
By adding 2-25 parts of the inorganic filler to 100 parts, the heat sealing strength of the lid material of the styrene-based resin container becomes 15
It always shows a strength of 1.0 kg / 15mm or more with respect to the heat sealing temperature of around 0 ° C, and does not cause cohesive failure when peeling off the heat-sealed lid material, and can form a heat-sealing resin layer that peels off at the interface. The inventors have found that a heat-sealing coating material is provided, and have reached the present invention.

The acrylic resin solution used in the present invention can be obtained by a known production method. That is, suspension polymerization, emulsion polymerization,
An acrylic resin produced by an arbitrary method such as a bulk polymerization method is selected and dissolved in an appropriate organic solvent, or a monomer of an acrylic resin component is solution-polymerized in an appropriate organic solvent by solution polymerization. The resulting acrylic resin solution is used.

As the monomer which is a constituent component of the acrylic resin, a known monomer generally used for producing an acrylic resin can be used. A typical example is C1-18 alkyl (meth) acrylate, but other monomers such as styrene, acrylonitrile, and vinyl acetate are copolymerizable and have a secondary transition point of a homopolymer of about 20 ° C. or more. Monomers having a functional group other than the hard monomer and (meth) acrylic acid, for example, polymerizable carboxylic acids such as itaconic acid, crotonic acid and fumaric acid, methylol (meth) acrylamide alkyl ethers, hydroxyalkyl ( (Meth) acrylates and glycidyl (meth) acrylates.

The acrylic resin is not particularly limited, but those having an excessively low softening point should be avoided because of the possibility of blocking.

Known inorganic fillers used in paints and printing inks can be used. Among them, for example, silica, talc, clay, precipitated sulfuric acid barium, alumina, calcium carbonate, zinc oxide, etc. What is called is preferable because it has a sense of transparency. However, other colored pigments and the like can be freely used if necessary.

(Function and Effect) The ratio of the inorganic filler used in the heat-sealing coating material for bonding a styrenic resin of the present invention is suitably in the range of 2 to 25 parts with respect to 100 parts of the nonvolatile content of the acrylic resin solution.

When the addition amount of the inorganic filler is less than 2 parts with respect to 100 parts of the non-volatile content of the acrylic resin solution, the heat sealing strength is not sufficiently improved. The tendency to occur is not improved. On the other hand, when the amount exceeds 25 parts, the heat sealing temperature rises and the heat sealing is not sufficiently performed, so that the heat sealing strength decreases.

 Hereinafter, the present invention will be described in more detail with reference to examples and the like.

Reference Example (Production Example of Acrylic Resin Solution A) In a 1-liter four-necked flask equipped with a stirrer, a reflux condenser, a dropping funnel, and an inert gas inlet tube, the following formulation A, B, C, D, E and F are charged, stirring is started, and the atmosphere is replaced by gently introducing nitrogen gas from an inert gas introduction pipe.

A N-butyl acrylate 94.0 g. B Methyl methacrylate 300.0 g. C Acrylic acid 6.0 g. D Ethyl acetate 320.0 g. E Toluol 240.0 g. F Azobisisobutyronitrile 2.4 g. To raise the internal temperature of the flask to 70 ° C
And kept at 70 ° C. for 2 hours. Subsequently, the temperature was raised to 80 ° C. and maintained for 5 hours, and then raised to 90 ° C., and after 3 hours, 20.0 g of ethyl acetate and 20.0 g of toluene.
Was added and cooled to obtain an acrylic resin solution A.

 The nonvolatile content was 40.5% and the viscosity was 10 poise.

(Production Example of Acrylic Resin Solution B) In the same flask as in the production example of the acrylic resin solution A, A, B, C, E, and F, excluding D, were added among the following composition A to F, Stirring is started, and the atmosphere in the flask is replaced with nitrogen gas.

A Methyl methacrylate 260.0 g. B Styrene 31.0 g. C Methacrylic acid 9.0 g. D Benzoyl peroxide 3.6 g. E Methyl ethyl ketone 300.0 g. F Toluol 200.0 g. Heat to raise the internal temperature of the flask to 75 ° C. Immediately, half of a solution prepared by dissolving 3.6 g of D benzoyl peroxide in 100.0 g of separately prepared toluene, ie, 51.8 g, was added at a time from a dropping funnel to start the reaction, and the mixture was kept at 75 ° C. for 2 hours. The temperature was raised to 80 ° C. and maintained for 10 hours to complete the reaction. During this time, it took 5 hours from the point when the temperature reached 80 ° C., and the remainder of the toluene solution of benzoyl peroxide was
51.8 g. Are added evenly. After completion of the reaction, 100.0 g of methyl ethyl ketone is added, and the mixture is cooled to obtain an acrylic resin varnish.

The acrylic resin varnish was taken out, and 150 g of a 30% solution of a separately prepared mixed solvent of vinyl chloride-vinyl acetate copolymer (Vinylit VMCH manufactured by UCC, USA) in a mixed solvent of ethyl acetate / methyl ethyl ketone (1: 1) was added and mixed. An acrylic resin solution B was obtained.

 It had a nonvolatile content of 29.8% and a viscosity of 11.3 poise.

Example 1 300 g of the acrylic resin solution A of the reference example was weighed, and talc powder (Microace L-1 manufactured by Nippon Talc Co., Ltd.) was added to 2 g of the talc powder.
7.6 g. The mixture was dispersed for 20 minutes using a batch type tabletop sand mill having a capacity of 800 cc to obtain a heat-sealing coating agent.

This heat-sealable coating agent is applied to a soft aluminum foil having a thickness of 50 μm so that the dry coating amount is about 5 g / m ^2, and then heat-dried in a drying furnace at an ambient temperature of 180 ° C. for 10 seconds to be heat-sealed. A coated aluminum foil having a conductive resin layer formed thereon was prepared.

Next, the obtained coated aluminum foil was applied to a high-impact polystyrene (HIPS) sheet having a thickness of 0.5 mm (available from Asahi Dow; Styron # 470) at a heat sealing temperature of 1 respectively.
Heat sealing was performed at 30 ° C., 150 ° C. and 170 ° C. under the conditions of a pressure of 3.0 kg / cm ² and a pressure bonding time of 1.0 second to obtain a heat sealed strength measurement molten sample.

Using the autograph (manufactured by Shimadzu Corporation) for the heat sealing strength measurement sample, a 180 degree peel test (pulling speed 200
mm / min.), heat sealing temperature 130 ℃, 150 ℃ and 170 ℃
Are 1,177, 1,180 and 1,22, respectively.
A value of 0 g./15 mm was obtained.

Peeling occurred between the aluminum foil and the heat-sealing resin layer, and there was no tendency to cause cohesive failure and fringing.

At least at a heat sealing temperature of about 150 ° C., a heat sealing strength of 1,000 g./15 mm or more is considered to be sufficient for practical use, so the above value is satisfactory.

Example 2 The same operation as in Example 1 was carried out except that the amount of talc powder was changed to 6.0 g. As a result of a 180 ° peel test on a sample for measuring heat sealing strength, a heat sealing temperature of 130 ° C., 15 ° C.
For 0 ° C and 170 ° C, respectively, 1,047, 1,173 and
A strength of 1,310 g./15 mm was obtained.

In addition, peeling occurred between the aluminum foil and the heat-sealing resin layer, and there was no tendency to cause cohesive failure and to leave an edge.

Comparative Example 1 The same operation was performed as in Example 1, except that 36.0 g of talc powder was added, exceeding the upper limit of the range of the addition amount of the present invention. The results of the 180-degree peel test on the sample for measuring the heat sealing strength show that all the peeled surfaces have occurred between the aluminum foil and the heat-sealing resin layer, and no cohesive failure has occurred. The strengths at 150 ° C. and 170 ° C. were only 447, 568 and 660 g./15 mm, respectively.

Comparative Example 2 The same operation as in Example 1 was performed without adding talc powder.

The results of the 180-degree peel test on the sample for measuring the heat sealing strength are as follows.
In the case of the above, only the strengths of 693, 840 and 943 g./15 mm were obtained, respectively, and the peeling was caused by cohesive failure in the heat-sealing resin layer, and the peeled surface had an edge residue.

Example 3 In Example 1, 400 g of the acrylic resin solution B of the reference example was used in place of the acrylic resin solution A, and 6.0 g of silica powder (manufactured by Fuji Devison; Siloid # 24) was added instead of talc powder. In the same manner as in Example 1, a sample for measuring heat sealing strength was prepared.

For the heat seal strength measurement sample,
A 180-degree peel test was performed. The heat-sealing strength at 130 ° C, 150 ° C and 170 ° C was 1,251, respectively.
Values of 1,366 and 1,420 g./15 mm were obtained.

Peeling occurred between the aluminum foil and the heat-sealing resin layer.

Example 4 A heat seal strength measurement sample was obtained in the same manner as in Example 3 except that 24.0 g of sedimentable barium sulfate was used instead of silica powder as the inorganic filler, and a 180 ° peel test was performed. The strengths at temperatures of 130 ° C, 150 ° C and 170 ° C were 1,105, 1,237 and 1,34, respectively.
A value of 0 g./15 mm was obtained.

The peeled surface was between the aluminum foil and the heat-sealing resin layer, and no margin was observed.

Example 5 A heat sealing strength measurement sample was obtained in the same manner as in Example 3, except that 12.0 g of Zinhua No. 2 was used instead of silica powder as the inorganic filler. 180 degree peeling test is as strength as heat sealing temperature 130 ℃, 150 ℃ and 170 ℃.
Values of 1,310, 1,384 and 1,417 g./15 mm, respectively, were obtained.

The peeled surface was between the aluminum foil and the heat-sealing resin layer, and no cohesive failure of the heat-sealing resin layer was observed.

Claims (1)

(57) [Claims] 1. A heat-sealing coating agent for bonding a styrene resin, comprising 2 to 25 parts of an inorganic filler added to 100 parts (parts by weight, hereinafter the same) of a nonvolatile content of the acrylic resin solution.