JP2908192B2 - Polyester film for metal plate lamination processing - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester film for laminating and forming a metal plate, and more particularly, it exhibits excellent formability when laminating to a metal plate and performing can forming such as drawing. Polyester film for metal plate lamination that can be used to produce metal cans having good heat resistance, and excellent heat resistance, retort resistance, fragrance preservation and flavor, impact resistance, etc., such as beverage cans and food cans About.

[0002]

2. Description of the Related Art Metal cans are generally coated to prevent corrosion of the inner and outer surfaces. Recently, for the purpose of simplifying the process, improving hygiene, and preventing pollution, rust prevention is performed without using an organic solvent. Development of a method for obtaining the property has been advanced, and as one of the methods, coating with a thermoplastic resin film has been attempted. That is,
Studies have been made on a method of laminating a thermoplastic resin film on a metal plate such as tin, tin-free steel, or aluminum, and then forming the can by drawing or the like. Polyolefin films and polyamide films have been tried as this thermoplastic resin film, but they do not satisfy all of moldability, heat resistance, fragrance preservation, and impact resistance.

On the other hand, polyester films, particularly polyethylene terephthalate films, have been attracting attention as having balanced properties, and some proposals based on these have been made. That is, (A) a biaxially oriented polyethylene terephthalate film is laminated on a metal plate via a low-melting-point polyester adhesive layer and used as a can-making material (JP-A-56-1045).
No. 1, JP-A-1-192546). (B) Amorphous or extremely low-crystalline aromatic polyester film is laminated on a metal plate and used as a can-forming material (JP-A-1-192545, JP-A-2-57).
339). (C) A biaxially oriented polyethylene terephthalate film having a low orientation and thermally fixed is laminated on a metal plate and used as a can-making material (Japanese Patent Application Laid-Open No. 64-22530).

[0004] However, the present inventors' studies have revealed that no satisfactory characteristics can be obtained in any case, and that each has the following problems.

Regarding (A), a biaxially oriented polyethylene terephthalate film is excellent in heat resistance and fragrance retention,
In the process of making cans with insufficient molding workability and large deformation, whitening (generation of minute cracks) and breakage of the film occur.

As for (B), since it is an amorphous or extremely low-crystalline aromatic polyester film, the moldability is good, but the fragrance retention is inferior, and the printing and retort sterilization after can-making are performed. Such a film may be easily embrittled by post-treatments or storage for a long period of time, and may be changed to a film which is easily broken by an impact from the outside of the can.

As for (C), the effect is not exhibited in the intermediate region between the above (A) and (B), but it has not yet reached the low orientation applicable to can processing. Even if it can be processed in a region with a small degree of deformation, subsequent printing,
As in the case of (B), there is a possibility that the retort treatment for sterilizing the contents of the can makes the film brittle easily and the film is likely to be broken by an impact from the outside of the can.

In order to solve such a problem, the present inventors have considered various uses of a film made of a copolymerized polyester and have made various studies. As a result, the copolymerized polyester film is excellent in molding processability, heat resistance, retort resistance, and fragrance retention, but has good taste retention, impact resistance, especially impact resistance at a low temperature of 15 ° C. or less. It is insufficient, and it has been found that when the metal can to which the film is bonded is dropped at a low temperature to give an impact, the film is easily cracked. Poor impact resistance at low temperatures poses a major problem when handled in a cooled state, such as metal cans for juices and soft drinks.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to improve the impact resistance of a copolymerized polyester film while maintaining the excellent moldability, heat resistance, retort resistance and fragrance retention. In particular, it is an object of the present invention to provide a polyester film for metal plate laminating and forming, which hardly causes cracks due to impact at a low temperature and does not deteriorate the taste of soft drinks and the like.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, have found that a film is composed of a copolymer polyester containing ethylene terephthalate as a main repeating unit and butylene terephthalate as a main repeating unit. It is composed of two layers including a polyester composition layer in which polyester and a specific ratio are blended, the surface roughness of each layer is in a specific range, and a germanium compound is used as a polymerization catalyst for a copolymerized polyester having ethylene terephthalate as a main repeating unit. The present inventors have found that the use of the compound significantly improves the impact resistance and taste retention at low temperatures, and that the winding property can be prevented from deteriorating.

That is, the present invention has a melting point of 210 to 245.
C., a copolymerized polyester layer (A) having a glass transition temperature of 60 ° C. or more, and a copolymerized polyester having a melting point of 210 to 245 ° C. and having ethylene terephthalate as a main repeating unit and produced using a germanium compound as a polymerization catalyst. (I) 80 to 45% by weight and melting point of 180 to 223
And a polyester layer (B) comprising a polyester composition containing 20 to 55% by weight of a polyester (II) containing butylene terephthalate as a main repeating unit at a temperature of 5 ° C., and a surface of the copolymerized polyester layer (A). A polyester film for laminating and processing metal sheets, characterized in that the roughness (Ra) is 15 nm or less and the surface roughness (Ra) of the polyester layer (B) is 15 nm or more.

In the present invention, a typical example of the copolymerized polyester used as the copolymerized polyester (I) in the copolymerized polyester layer (A) and the polyester layer (B) is copolymerized polyethylene terephthalate. The copolymer component may be an acid component or an alcohol component. Examples of the acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decane dicarboxylic acid, and alicyclic groups such as cyclohexanedicarboxylic acid. Examples of the dicarboxylic acid include aliphatic alcohols such as butanediol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

Although the proportion of the copolymer component depends on the type, it results in a melting point of 210 to 245 ° C., preferably 215 ° C.
It is the ratio which becomes the range of -235 ° C. If the melting point is lower than 210 ° C., the heat resistance will be poor. On the other hand, the melting point is 245 ° C
If it exceeds 300, the crystallinity of the polymer is too large and the moldability is impaired.

Here, the melting point of the copolyester was measured by Du Pont Instruments 910.
A method in which a melting peak is determined at a heating rate of 20 ° C./min using DSC. The sample amount is about 20 mg.

The intrinsic viscosity of the copolyester is preferably from 0.52 to 0.80, more preferably from 0.54 to 0.70.

Further, the copolymerized polyester constituting the copolymerized polyester layer (A) in the present invention needs to have a glass transition temperature of 60 ° C. or higher, preferably 70 ° C. or higher. When the secondary transition point is lower than 60 ° C., satisfactory scent retention cannot be obtained. As such a copolymerized polyester, a copolymerized polyester having a high glass transition temperature can be obtained, and thus isophthalic acid copolymerized polyethylene terephthalate is particularly preferable.

The copolymerized polyester containing ethylene terephthalate as a main repeating unit in the present invention may be either a direct weight method or a DMT method (transesterification method). In the case of the DMT method, a manganese compound is used as a transesterification catalyst. (Eg, manganese acetate) or a titanium compound (eg, titanium acetate, titanium tetrabutoxide, etc.)
It is preferable to use In the polymerization step, a germanium compound is used as a polymerization catalyst. Examples of the germanium catalyst include (a) amorphous germanium oxide (b) fine crystalline germanium oxide (c) a solution of germanium oxide dissolved in glycol in the presence of an alkali metal or alkaline earth metal or a compound thereof (d) oxidation A solution in which germanium is dissolved in water is used.

The amount of the germanium compound catalyst is 40 to 40 as the amount of germanium remaining in the copolymerized polyester.
200 ppm is preferable, and 60 to 150 ppm is more preferable.

[0019] The copolyester methyl ends concentration of preferably less 15eq mol / 10 ⁶ g in the polyester, the following further 10eq mol / 10 ⁶ g is preferred.
If the concentration of methyl terminals in the polyester is too high, phenomena such as easy formation of white powder from the copolymerized polyester during molding processing, or in the case of a container, poor taste retention may be observed.

In the present invention, the polyester (II) constituting the polyester layer (B) is a polyester having butylene terephthalate as a main repeating unit, and may be a homopolymer or a copolymer.

The copolymer component in the copolymer may be an acid component or an alcohol component. Examples of the copolymeric acid component include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, and decane dicarboxylic acid, and fatty acids such as cyclohexanedicarboxylic acid. Examples of the cyclic dicarboxylic acid include aliphatic diols such as ethylene glycol and hexanediol, and alicyclic diols such as cyclohexanedimethanol. These can be used alone or in combination of two or more.

The proportion of the copolymer component depends on the type, but as a result, the melting point is 180 to 223 ° C., preferably 2
The ratio is in the range of 00 to 223 ° C, more preferably 210 to 223 ° C. If the melting point is lower than 180 ° C., the heat resistance will be poor. The melting point of the polybutylene terephthalate homopolymer is 223 ° C.

The measurement of the melting point of this polyester was carried out in the same manner as in the measurement of the above-mentioned copolymerized polyester.
Performed using Instruments 910 DSC.

In the polyester film of the present invention,
The polyester layer (B) is composed of 80 to 45% by weight, preferably 70 to 45% by weight of a copolymerized polyester mainly composed of polyethylene terephthalate and having a melting point of 210 to 245 ° C.
More preferably, it is 59 to 50% by weight, and is a polybutylene terephthalate or a copolymer polyester mainly composed of polybutylene terephthalate and having a melting point of 180 to 223 ° C.
It must be 55% by weight, preferably 30-55% by weight, more preferably 41-50% by weight. If the content of polybutylene terephthalate or polybutylene terephthalate copolyester is less than 20% by weight and the content of polyethylene terephthalate copolyester exceeds 80% by weight, the impact resistance at low temperatures cannot be improved. When the content of polybutylene terephthalate or the copolymer of polybutylene terephthalate exceeds 55% by weight and the content of the polyethylene terephthalate copolymerized polyester is less than 45% by weight, the heat resistance of the film decreases and the impact resistance becomes insufficient.

In the present invention, the copolyester used for the copolyester (I) of the copolyester layer (A) and the polyester layer (B) and the polyester used for the polyester (II) of the polyester layer (B) are: It is not limited by the manufacturing method.
For example, in the case of a copolymerized polyester mainly composed of polyethylene terephthalate, a method in which terephthalic acid, ethylene glycol and a copolymer component are subjected to an esterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to form a copolymerized polyester, or Preferably, a method is used in which dimethyl terephthalate, ethylene glycol and a copolymer component are subjected to a transesterification reaction, and then the obtained reaction product is subjected to a polycondensation reaction to obtain a copolymerized polyester. In the production of each copolymerized polyester and polybutylene terephthalate, if necessary, other additives, for example, an antioxidant,
Heat stabilizers, ultraviolet absorbers, antistatic agents and the like can also be added.

The surface roughness (Ra) of the copolymerized polyester layer (A) must be 15 nm or less. Preferably 12 nm or less, more preferably 10 n
m or less. The copolyester layer (A) is a layer located on the side in contact with the contents of the can when bonded to a metal can. By adjusting the surface roughness (Ra) to 15 nm or less, the contents, especially It is possible to prevent the taste of the soft drink from becoming worse.

In order to make the surface roughness (Ra) 15 nm or less, the average particle size and the amount of the lubricant to be added to the copolymerized polyester may be appropriately selected. For example, when silica is used as a lubricant, 0.04% by weight or less for silica having an average particle diameter of 1.5 μm, and 0.36% by weight or less for silica having an average particle diameter of 0.8 μm. . When the addition amount is 0.2% by weight, the average particle size of silica is 0.9%.
When the addition amount is 5 μm or less and the addition amount is 0.05% by weight, the average particle size of the silica may be 1.33 μm or less. In this case, lubricants having different types and average particle diameters may be mixed and used.

Further, the polyester layer (B) needs to have a surface roughness (Ra) of 15 nm or more.
If the surface roughness (Ra) is less than 15 nm, the handling (winding) of the film deteriorates, which is not appropriate.

The polyester layer (B) is a layer which is bonded to the metal can when the film is bonded to the metal can.
Since there is no direct contact with the contents of the can, the surface roughness (R
Even if a) is 15 nm or more, the taste of the contents is not deteriorated.

In the case of the polyester layer (B), a desired surface roughness (Ra) can be obtained by appropriately controlling the average particle size and the amount of the lubricant added to the copolymerized polyester.

The lubricant to be added to the copolymerized polyester layer (A) and the polyester layer (B) may be inorganic or organic, but inorganic is preferred. As an inorganic lubricant,
Silica, alumina, titanium dioxide, calcium carbonate, barium sulfate and the like can be exemplified. As the organic lubricant, silicone resin particles, crosslinked polystyrene particles and the like can be exemplified. In particular, a lubricant which is preferable in terms of pinhole resistance is a monodispersed lubricant having a particle size ratio (major axis / minor axis) of 1.0 to 1.2. Examples of such a lubricant include spherical silica, spherical silicone resin particles, and spherical cross-linked polystyrene.

The film has a surface roughness (Ra) of J
This is the center line average roughness determined according to IS-B0601, and a portion of the measured length L is extracted from the film surface roughness curve in the direction of the center line, the center line of the extracted portion is defined as the X axis, and the longitudinal magnification Is the Y axis, and the roughness curve is Y =
When represented by f (x), the value (R
a: nm) is defined as the film surface roughness.

[0033]

(Equation 1)

In the present invention, when the reference length is 2.5 mm, 5
The number is measured, and Ra is represented as an average of four values excluding one from the larger value.

The polyester film of the present invention has a structure in which a copolymerized polyester layer (A) and a polyester layer (B) are laminated. Such a film having a two-layer structure comprises, for example, respective layers. The copolymerized polyester and the polyester composition are separately melted, co-extruded, laminated and fused before solidification, then biaxially stretched, a method of heat setting, the copolymerized polyester and the polyester composition are separately melted and extruded. It can be manufactured by a method of forming a film, unstretched state or after stretching, and laminating and fusing them.

The polyester film has a surface roughness (R
a) When it is composed of only the copolymerized polyester layer (A) having a thickness of 15 nm or less, the impact resistance at low temperature becomes insufficient, and the handling property (winding property) further deteriorates. Conversely, when the surface roughness (Ra) is composed of only the polyester layer (B) having a thickness of 15 nm or more, the taste retention is deteriorated, and the taste of the contents of the can is deteriorated.

The polyester film of the present invention may be an unstretched film, but is usually used in a state of being biaxially stretched and heat set. In this case, the refractive index in the thickness direction of the copolymerized polyester layer (A) is 1.505 to 1.55.
It is preferably 0, more preferably more than 1.510 and not more than 1.540. If the refractive index is too low, the moldability will be insufficient, while if it is too high, the structure will be close to amorphous and the heat resistance may decrease.

[0038] The polyester film of the present invention preferably has a thickness of 6 to 75 µm. 10-75μ
m, particularly preferably 15 to 50 μm. If the thickness is less than 6 μm, breakage or the like is likely to occur during processing, while if it exceeds 75 μm, the quality is excessive and uneconomical.

The thickness T of the copolymerized polyester layer (A)
The ratio of the _A, and the thickness T _B of the polyester layer (B) (T _A /
T _B) is preferably about 0.02 to 0.67, more preferably 0.04 to 0.43, particularly preferably 0.04
０．２0.25. Specifically, for example, the thickness is 25 μm
Polyester layer (B)
Is 0.5 to 10 μm, preferably 1 to 7.5 μm.
m, more preferably 1 to 5 μm.

As the metal plate to which the polyester film of the present invention is bonded, in particular, a metal plate for can making, a plate of tin, tin-free steel, aluminum or the like is suitable.
The bonding of the polyester film to the metal plate can be performed, for example, by the following method.

The metal plate is heated to a temperature equal to or higher than the melting point of the film, the film is laminated, and then cooled, and the surface layer (thin layer) of the film in contact with the metal plate is made amorphous and adhered.

A film is preliminarily coated with an adhesive layer by a primer, and this surface is bonded to a metal plate. As the adhesive layer, a known resin adhesive, for example, an epoxy-based adhesive,
Epoxy-ester adhesives, alkyd adhesives and the like can be used.

When the polyester film of the present invention is bonded to a metal plate, the surface roughness (Ra) is 15 n.
m or less so that the copolyester layer (A) of not more than m is in contact with the contents. For example, when bonding the polyester film of the present invention to the inside of a metal can, the side of the polyester layer (B) is bonded to the can.

Further, in the polyester film of the present invention, if necessary, another additional layer may be laminated between the copolymerized polyester layer (A) and the polyester layer (B) or on one side.

[0045]

The present invention will be further described with reference to the following examples.

[0046]

Examples 1 to 8 and Comparative Examples 1 to 7 90 parts by weight of dimethyl terephthalate, 10 parts by weight of dimethyl isophthalate,
70 parts by weight of ethylene glycol were charged into a reaction vessel, and 0.018 parts by weight of tetrabutyl titanate was further added.
A normal transesterification reaction was performed. Subsequently, 0.013 parts by weight of phosphoric acid was added, and then germanium dioxide was added to 0.1 part by weight.
027 parts by weight were added. Depressurize the reaction system and apply vacuum,
A normal polycondensation reaction was performed to obtain a copolymerized polyester.

Polyethylene terephthalate copolymerized with the components shown in Table 1 (containing 0.1% by weight of spherical silica having an intrinsic viscosity of 0.64, a particle size ratio of 1.1 and an average particle size of 0.3 μm)
Is a copolymerized polyester layer (A), a polyester composition also shown in Table 1 (particle size ratio is 1.1, average particle size is 1.5 μm)
m, each of which is separately dried and melted by a conventional method so as to become a copolymerized polyester layer (B) containing 0.1% by weight of spherical silica, and then co-extruded from dies adjacent to each other to form a laminate. It was fused and quenched and solidified to form an unstretched laminated film.

Next, the unstretched film was longitudinally stretched 3.0 times at 110 ° C., and then transversely stretched 3 times at 125 ° C.
It was heat-set at 190 ° C. to obtain a biaxially oriented laminated film.

The thickness of the obtained film was 25 μm, the thicknesses of the copolymerized polyester layer (A) and the copolymerized polyester layer (B) were 5 μm and 20 μm, respectively, and the surface roughness (Ra) was 7 nm and 25 nm, respectively. Met.

The surface roughness (Ra) was measured by a stylus type surface roughness meter (SURFCORDER S manufactured by Kosaka Laboratory Co., Ltd.).
E-30C) using a stylus radius of 2 μm and a measurement pressure of 0.0
The measurement was performed under the conditions of 3 g and a cutoff value of 0.25 mm.

[0051]

[Table 1]

[0052]

Comparative Examples 8 to 9 In Example 2, the thickness of only the copolymerized polyester layer (A) (Comparative Example 8) and the polyester layer (B) (Comparative Example 9) was 25 μm without forming a two-layer laminated structure.
Was produced.

[0053]

Examples 9 to 10 and Comparative Examples 10 to 11 In Example 2, the average particle size and amount of spherical silica contained in the copolymerized polyester layer (A) and the polyester layer (B) are shown in Table 2.
And the other conditions were the same as in Example 2 to obtain a biaxially oriented laminated film.

[0054]

[Table 2]

[0055]

Comparative Examples 12 to 14 In Examples 1 to 3, germanium dioxide was used as a polymerization catalyst with 0.06 g of antimony trioxide.
Except for changing to parts by weight, in the same manner as in Examples 1 to 3,
A biaxially stretched film was obtained.

A total of 21 kinds of films obtained in Examples 1 to 10 and Comparative Examples 1 to 14 were bonded to both sides of tin-free steel heated to 230 ° C. and having a plate pressure of 0.25 mm.
After cooling with water, the plate was cut into a disk having a diameter of 150 mm and deep-drawn in four stages using a drawing die and a punch to prepare a side-seamless container (hereinafter abbreviated as can) having a diameter of 55 mm.

The following observations and tests were performed on the cans, and the cans were evaluated according to the following standards.

(1) Deep drawing processability-1 ○: The film was processed without any abnormality, and no whitening or breakage was observed in the film. Δ: Whitening is observed at the top of the film can. X: Film breakage is observed in a part of the film.

(2) Deep drawing processability-2 ○: Processed without any abnormality, rust prevention test on film surface in can (1% NaCl water was put in the can, electrodes were inserted, and the can body was used as an anode. The current value when a voltage of 6 V is applied is measured.
Hereinafter, abbreviated as ERV test) shows 0.1 mA or less. ×: There is no abnormality in the film, but the current value is 0.1 mA or more in the ERV test, and pinhole-shaped cracks starting from the coarse lubricant are recognized in the film when the energized portion is observed under magnification.

(3) Impact resistance For cans with good deep drawing, pour water thoroughly, cool to 0 ° C., drop 10 pieces for each test from a height of 30 cm onto a PVC tile floor. As a result of the ERV test in the can, the results were as follows: A: 0.1 mA or less for all 10 samples. C: 0.1 mA or more for 1 to 5 pieces. X: The value was 0.1 mA or more for 6 or more pieces, or cracking of the film was already observed after dropping.

(4) Heat embrittlement resistance After the can which had been subjected to good deep drawing was heated and maintained at 200 ° C. for 5 minutes, the impact resistance evaluation described in (3) was performed. Was 0.1 mA or less. C: 0.1 mA or more for 1 to 5 pieces. ×: The film was cracked already at 0.1 mA or more for 6 or more pieces or after heating at 200 ° C. for 5 minutes.

(5) Retort Resistance The cans having good deep drawing properties were filled with water, retorted in a steam sterilizer at 120 ° C. for 1 hour, and then stored at 50 ° C. for 30 days. After dropping 10 cans for each test from a height of 50 cm onto a PVC tile floor, an ERV test in the cans was performed.

○: 0.1 mA or less for all 10 samples. C: 0.1 mA or more for 1 to 5 pieces. X: The value was 0.1 mA or more for 6 or more pieces, or cracking of the film was already observed after dropping.

(6) Preservation of Taste A can that had good deep drawing was filled with cider and sealed. After keeping at 37 ° C. for 30 days, the can was opened and the change in taste was examined by a sensory test. ：: There was no change in taste. Δ: Slight change in taste was observed. ×: A change in taste was observed.

The evaluation results and winding properties of the above 21 kinds of films are as shown in Table 3.

[0066]

[Table 3]

As is clear from the results shown in Table 3, cans using the polyester film of the present invention are excellent in deep drawability, heat embrittlement resistance, retort resistance, and fragrance retention, and also have impact resistance. In particular, it has excellent impact resistance at low temperatures, does not deteriorate the taste of soft drinks and the like, and has good winding properties.

[0068]

The film for laminating and processing metal sheets of the present invention has excellent moldability, heat resistance, retort resistance, and fragrance retention, and also has impact resistance, especially impact resistance at low temperatures. Is improved, the taste of soft drinks and the like is not deteriorated, and the winding property is also good. Therefore, it is particularly suitable for being used after being cooled and stuck to a metal can for soft drinks and the like which is often handled at a low temperature.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Takafumi Kudo 3-37-19 Koyama, Sagamihara-shi, Kanagawa Teijin Limited Sagamihara Research Center (56) References JP-A-5-338103 (JP, A) Hei 6-172556 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B32B 1/00-35/00

Claims (3)

(57) [Claims] 1. A copolymerized polyester layer (A) having a melting point of 210 to 245 ° C. and a glass transition temperature of 60 ° C. or higher,
Copolyester (I) 80 having a melting point of 210 to 245 ° C. and containing ethylene terephthalate as a main repeating unit and produced using a germanium compound as a polymerization catalyst
Polyester containing butylene terephthalate having a melting point of 180 to 223 ° C and a main repeating unit of up to 45% by weight.
I) a polyester layer (B) comprising a polyester composition blended with 20 to 55% by weight, and the copolymer polyester layer (A) having a surface roughness (Ra) of 15 n
m, wherein the polyester layer (B) has a surface roughness (Ra) of 15 nm or more. 2. The polyester film according to claim 1, wherein the copolymerized polyester layer (A) is made of isophthalic acid copolymerized polyethylene terephthalate. 3. The polyester film according to claim 2, wherein the isophthalic acid copolymerized polyethylene terephthalate is produced using a germanium compound as a polymerization catalyst.