JP3272928B2 - Filter media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filter medium, particularly a filter medium used for a pleated type cartridge filter, a depth type cartridge filter and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a filter medium used for a pleated type cartridge filter or a filter medium used for an inner layer which determines the filtration accuracy of a depth type cartridge filter is formed by melt-blowing so that fine particles can be collected. A dense filter medium having a small average pore diameter obtained by heating and pressing a nonwoven fabric is used. Although these filter media can obtain almost 100% of particles having a diameter on the order of several microns, they have a drawback that clogging easily occurs and the life of the filter media is short. On the other hand, there has been proposed a filter medium having a close-packed structure obtained by laminating melt-blown nonwoven fabrics having different fiber diameters and subjecting them to heat and pressure treatment. This filter medium has a slightly longer filter life than that obtained by heat and pressure treatment of the same fiber diameter.However, the melt blown nonwoven fabric of any fiber diameter has been considerably densified by the heat and pressure treatment. It was easily clogged, and a sufficient filtration life was not obtained. Further, attempts have been made to obtain a filter medium having a coarse-dense structure by laminating and integrating a melt-blown nonwoven fabric before the heat-press processing on the dense filter medium subjected to the heat-press processing. However, when the dense filter medium and the melt-blown nonwoven fabric are integrated using an adhesive or the like, the adhesive closes the openings of the dense filter medium, increasing the liquid flow resistance and shortening the filtration life. There is a problem and a problem that the adhesive flows out into the processing solution. Also, in the method of integrating the dense filter medium and the melt-blown nonwoven fabric by fiber bonding by heating and pressurizing treatment, the two are well integrated under the pressing conditions smaller than the pressing conditions used for producing the dense filter medium (joining). ), There is a problem that delamination occurs immediately when pleating or the like is applied. On the other hand, if the pressing condition is increased to the same level or more, a slight difference in density occurs, but both layers are densified. Couldn't be long enough.

[0003]

SUMMARY OF THE INVENTION As a result of studying these problems, the inventors of the present application have conducted a heating and pressurizing treatment in advance by heating a nonwoven fabric for a certain period of time and then pressurizing or heating and pressing. It has been found that the nonwoven fabric A can be integrated with the nonwoven fabric B that has been previously subjected to the heat and pressure treatment by fiber bonding even under a pressure condition smaller than the pressure condition of the heating and pressurizing treatment of the nonwoven fabric B, and the present invention has been completed. It has the ability to collect particles of the order of several microns, has a long filtration life, and has an average fiber diameter of 0.1 to
It is an object of the present invention to provide a filter medium having a close-packed structure in which two or more non-woven fabrics of different densities composed of fine fibers of about 10 μm are integrated.

[0004]

Means for Solving the Problems The present invention relates to a non-woven fabric A made of a fiber having an average fiber diameter of 0.1 to 10 μm and a non-woven fabric made by heating and pressing a non-woven fabric made of a fiber having an average fiber diameter of 0.1 to 10 μm. B and a non-woven fabric B. The present invention relates to a filter medium having a close-packed structure in which non-woven fabric A and non-woven fabric B are integrated by performing a pressure treatment under a pressure condition smaller than the heating and pressure treatment condition of non-woven fabric B after laminating B and heating.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The nonwoven fabric A is preferably a melt-blown nonwoven fabric or a hydroentangled nonwoven fabric mainly composed of splittable fibers, and the average fiber diameter of the constituting fibers is 0.1 to 10 μm.
m, particularly preferably 0.5 to 5 μm.

[0006] Melt blown nonwoven fabric is a nonwoven fabric produced by a melt blow method, which is particularly preferable because it has a small average fiber diameter and a small average pore diameter. As the melt-blown nonwoven fabric, those made of thermoplastic fibers such as polyolefin fibers such as polypropylene fibers and polyethylene fibers, polyester fibers, and polyamide fibers can be used, and those made of polyolefin fibers having excellent chemical resistance and the like are desirable.

[0007] The hydroentangled non-woven fabric mainly composed of splittable fibers is preferably one in which splittable fibers are split in an entangling step by a water flow and the fiber diameter after splitting is about 0.1 to 10 µm. As the splittable fibers, fibers in which resin components such as polypropylene / polyethylene, polypropylene / polyester, and polyamide / polyester are combined can be used. In particular, polypropylene / polypropylene having excellent chemical resistance and the like can be used.
A splittable fiber obtained by combining a resin component of polyethylene is desirable.

The basis weight of the nonwoven fabric A before lamination is 20 to 10
0 g / m ^2, more preferably it is desirable in the range of 30 to 80 g / m ^2, also apparent density 0.01
0.25 g / cm ³ is preferred, and
It is desirable to be in the range of 0.2 g / cm ³ .

The nonwoven fabric B has an average fiber diameter of 0.1 to 10 μm
This is a nonwoven fabric obtained by densifying a nonwoven fabric made of the above-mentioned fibers by heating and pressing, and a melt-blown nonwoven fabric or a hydroentangled nonwoven fabric mainly composed of splittable fibers is preferable. The melt-blown nonwoven fabric is particularly good because the fibers are not subjected to strong stretching in the manufacturing process, so that the fibers can be densified by heating and pressing to easily obtain a small average pore size.

The heating and pressurizing conditions vary depending on the type of fiber used. For example, in the case of polypropylene fiber, the temperature is 40 to 100 ° C., preferably 5 to 100 ° C.
Under heating conditions of 0 to 80 ° C, linear pressure of 30 to 300 kg / c
m, more preferably 50 to 200 kg / cm.

The basis weight of the non-woven fabric B before lamination is 20 to 10
0 g / m ^2, more preferably it is desirable in the range of 30 to 80 g / m ^2, also the apparent density from 0.4 to 0.
7 g / cm ³ is preferred, and in particular, 0.45 to 0.65
g / cm ³ . The average fiber diameter of the nonwoven fabric A and the nonwoven fabric B is desirably the same or almost the same for a filter medium used for a pleated cartridge filter that requires particularly high filtration accuracy.

After laminating nonwoven fabric A and nonwoven fabric B and heating,
The processing conditions for pressurization vary depending on the type of the fiber constituting the nonwoven fabric. For example, when the nonwoven fabric is made of a polypropylene-based fiber, the heating condition is preferably a temperature of 40 to 100 ° C,
In particular, the heating temperature is desirably in the range of 50 to 80 ° C, and the heating time is 10 to 60 seconds, more preferably 10 to 40 seconds.
Desirably in the range of seconds. The condition of the pressure applied after the above-mentioned heating needs to be lower than the pressure condition at the time of producing the nonwoven fabric B, and the linear pressure is desirably 5 to 50 kg / cm, preferably 10 to 30 kg / cm. If the pressure condition is higher than the pressure condition at the time of producing the nonwoven fabric B, the obtained filter medium becomes too dense. Note that the pressure treatment may be a heating and pressure treatment.

The basis weight of the obtained filter medium is 40 to 200 g / m.
² , preferably 60 to 160 g / m ² , and an apparent density of 0.
2 to 0.6 g / cm ³ , preferably 0.3 to 0.5 g / cm ³
It is desirably in the range of cm ³ .

Since the filter medium of the present invention is heated or pressurized after heating the nonwoven fabric for a certain period of time, even under a pressure condition smaller than the pressurization condition of the heating and pressurizing process of the nonwoven fabric B previously heated and pressurized, The nonwoven fabric A and the nonwoven fabric B can be integrated by fiber bonding. For this reason, since only a small pressure is applied to the nonwoven fabric A, the nonwoven fabric A is not very densified,
Compared with the nonwoven fabric B, the filter material is in a rough state, and a filter medium having a structure with a difference in density is obtained.

Hereinafter, the present invention will be described specifically with reference to examples.

【Example】

Example 1 By a melt blown method, a basis weight of 40 g / m ² and a thickness of 0.
70 mm, density 0.057 g / cm ³ , average fiber diameter 1.
A 7 μm polypropylene melt-blown nonwoven fabric 1 was produced. The nonwoven fabric 1 is heated and pressed by a pressure roll having a surface temperature of 60 ° C. under a condition of a linear pressure of 200 kg / cm to obtain a basis weight of 40 g / m ² , a thickness of 0.06 mm, and a density of 0.6.
Non-woven fabric 2 of ³ g / cm ³ was produced. Immediately after the nonwoven fabric 1 and the nonwoven fabric 2 were preheated at 100 ° C. for about 30 seconds, they were pressed at a linear pressure of 20 kg / cm with a pressure roll having a surface temperature of 100 ° C. to obtain a basis weight of 80 g / m ² and a thickness of 80 g / m ² . 0.20 mm, density 0.40 g / cm ³ , average pore size 1.
A 0 μm filter medium was produced.

COMPARATIVE EXAMPLE 1 Two non-woven fabrics 1 of Example 1 were laminated at a surface temperature of 6
It was heated and pressed by a pressure roll at 0 ° C. under the condition of a linear pressure of 100 kg / cm to give a basis weight of 80 g / m ² and a thickness of 0.13.
A filter medium having a diameter of 1.0 mm, a density of 0.62 g / cm ³ and an average pore diameter of 1.0 μm was prepared.

Comparative Example 2 The nonwoven fabric 1 of Example 1 was heated and pressed by a pressing roll having a surface temperature of 60 ° C. under the condition of a linear pressure of 50 kg / cm.
40g / m ² , thickness 0.08mm, density 0.50g
/ Cm ³ of nonwoven fabric 3 was produced. A laminate of the nonwoven fabric 1 and the nonwoven fabric 3 of Example 1 was heated and pressed by a pressure roll having a surface temperature of 60 ° C. under the condition of a linear pressure of 50 kg / cm to obtain a basis weight of 80 g / m ² and a thickness of 0.14 mm. , Density 0.5
A filter medium having 7 g / cm ³ and an average pore diameter of 1.1 μm was prepared.

Example 2 Splittable fiber composed of a polypropylene component and a polyethylene component, which can be divided into eight (denier 2 denier, fiber length 45 mm)
100% by weight of a fibrous web is subjected to a hydroentanglement treatment,
Weight 60g / m ² , thickness 0.34mm, density 0.18g
/ Cm ³ , and a nonwoven fabric 4 having an average fiber diameter of 3.5 μm. This nonwoven fabric 4 is heated and pressed by a pressure roll having a surface temperature of 60 ° C. under a linear pressure of 200 kg / cm.
Basis weight 60g / m ² , thickness 0.12mm, density 0.50g
/ Cm ³ of nonwoven fabric 5 was produced. Immediately after pre-heating the non-woven fabric 4 and the non-woven fabric 5 at 100 ° C. for about 30 seconds, a linear pressure of 2 was applied by a pressure roll having a surface temperature of 100 ° C.
It is pressurized at 0 kg / cm, and has a basis weight of 120 g / m ² and a thickness of 0.
33 mm, density 0.36 g / cm ³ , average pore size 2.3 μ
m were prepared.

COMPARATIVE EXAMPLE 3 Two nonwoven fabrics 4 of Example 2 were laminated at a surface temperature of 6.
It was heated and pressed by a pressure roll at 0 ° C. under the condition of a linear pressure of 100 kg / cm to give a basis weight of 120 g / m ² and a thickness of 0.2 g / m ² .
2 mm, density 0.55 g / cm ³ , average pore size 2.2 μm
Was prepared.

Example 3 Immediately after preheating at 100 ° C. for about 30 seconds, two nonwoven fabrics 4 of Example 2 and nonwoven fabric 2 of Example 1 were laminated.
With a pressure roll with a surface temperature of 100 ° C, a linear pressure of 20 kg /
cm under heat and pressure conditions, the basis weight is 100 g / m ² ,
A filter medium having a thickness of 0.23 mm, a density of 0.43 g / cm ³ and an average pore diameter of 1.2 μm was prepared.

Comparative Example 4 The nonwoven fabric 1 of Example 1 was heated and pressed by a pressing roll having a surface temperature of 60 ° C. under a linear pressure of 100 kg / cm to obtain a basis weight of 40 g / m ² and a thickness of 0.09 mm. Density 0.4
A nonwoven fabric 6 of 4 g / cm ³ was produced. A laminate of the nonwoven fabric 4 and the nonwoven fabric 6 of Example 2 was heated and pressed by a pressure roll having a surface temperature of 60 ° C. under a linear pressure of 100 kg / cm to obtain a basis weight of 100 g / m ² and a thickness of 0.16 mm. And a filter medium having a density of 0.63 g / cm ³ and an average pore diameter of 1.1 μm.

The filtration performance of the filter media obtained in each of these Examples and Comparative Examples was examined by the following method. The results are shown in Table 1.

(Water resistance) Water is filtered through a filter medium (effective area 51.5).
cm ² ), the pressure loss when water was passed from the rough side of the filter medium at a flow rate of 3 liter / min was measured and defined as water flow resistance. (Removed particle diameter) While uniformly stirring a test solution having a concentration of 10 ppm in which JIS 11 dust is dispersed in water, water is passed through the filter medium (effective area 51.5 cm ² ) at a flow rate of 3 liters / minute from the coarse side of the filter medium. One minute after the start of water flow, the filtrate was collected, and the number of particles contained in the filtrate and the test solution before filtration was measured for each particle size using a particle size distribution analyzer, and collected at each particle size. The efficiency was determined by the following equation. The smallest particle diameter (μm) among the particle diameters exhibiting a collection efficiency of 100% was defined as the particle diameter from which the filter medium was removed.

Collection efficiency (%) = (AB) × 100 / A A is the number of particles before filtration, and B is the number of particles after filtration. (Filtration life) Concentration of JIS 11 dust dispersed in water 1
While uniformly stirring the test solution of 0 ppm, water was passed through the filter medium (effective area 51.5 cm ² ) at a flow rate of 3 liter / min from the rough side of the filter medium, and the pressure loss was sequentially measured for each water flow rate. The total amount of water passed until the pressure difference from the initial pressure became 2 kg / cm ² was defined as the filtration life.

[0025]

Table 1 Water flow resistance Removal particle diameter Filtration life (kg / cm ² ) (μm) (L) Example 1 0.25 2.0 120 Comparative Example 1 0.43 2.2 66 Comparative Example 2 0.39 2.3 72 Example 2 0.12 3.3 300 Comparative Example 3 0.23 3.1 183 Example 3 0.27 1.8 115 Comparative Example 4 0.42 2.2 65

Comparing Example 1 with Comparative Examples 1 and 2, Example 2 with Comparative Example 3, and Example 3 with Comparative Example 4, the filter media of Examples 1, 2 and 3 have a rough and dense structure, and Since the density is small, the filtration accuracy is high, the processing flow rate is large, and the filtration life is long. In contrast, Comparative Examples 1, 2, and 3
And 4 each have an average pore diameter equivalent to that of Examples 1, 2 and 3, so that the filtration accuracy shows a value equivalent to that of the invention of this application, but the water flow resistance is large, and It was easily clogged and had a remarkably short filtration life. Since the filter medium of the present invention has a layer having high filtration accuracy and a layer coarser than that, it has low liquid permeation resistance, can process at a high flow rate, is hardly clogged, and has a long service life. Excellent collection efficiency.

Examples 4 to 6 and Comparative Examples 5 to 8 (pleated cartridge filters) The filter media obtained in Examples 1 to 3 and Comparative Examples 1 to 4 were prepared by a spun bond method with a basis weight of 40 g / m ² , Thickness 0.
It is sandwiched between two 34 mm polypropylene spunbonded nonwoven fabrics, pleated with a folding width of 15 mm, and wrapped around a cylindrical porous core one round so that the number of filter media is 80, and the inner diameter is 3 cm. , 6.5cm outside diameter, length 2
A 5 cm pleated cartridge filter was prepared. These pleated cartridge filters were mounted on the housing of a liquid filtration device, and the filtration performance was examined by the following method. The results are shown in Table 2. (Water flow resistance) Pressure loss when water was passed through the cartridge filter at a flow rate of 25 liter / min was measured and defined as water flow resistance. (Removed particle size) While uniformly stirring a test solution having a concentration of 10 ppm in which JIS 11 kinds of dust is dispersed in water, water is passed through the cartridge filter at a flow rate of 25 L / min, and a filtrate one minute after the start of water flow is collected. Then, the number of particles contained in the filtrate and the test solution before filtration was measured for each particle using a particle size distribution analyzer, and the collection efficiency at each particle size was determined by the following equation. Among the particle diameters showing 100% collection efficiency,
The smallest particle size (μm) was taken as the particle size removed by the cartridge filter. Collection efficiency (%) = (AB) × 100 / A Here, A is the number of particles before filtration, and B is the number of particles after filtration. (Filtration life) Concentration 2 of JIS 11 dust dispersed in water
While uniformly stirring the test solution of 0 ppm, water was passed through the cartridge filter at a flow rate of 25 liters / minute, and the pressure loss was sequentially measured with respect to each flow rate, and the differential pressure from the initial pressure was 2 kg / cm ² . The total amount of water that had been processed until this time was determined as the filtration life.

[0028]

[Table 2] Filter media used Water flow resistance Removal particle size Filtration life [kg / cm ² ] [μm] [liter] Example 4 Filter media of Example 1 0.22 1.9 7980 Comparative Example 5 Filter media of Comparative Example 1 0 .45 2.2 3900 Comparative Example 6 Filter Material of Comparative Example 2 0.40 2.1 4400 Example 5 Filter Material of Example 2 0.14 3.2 10250 Comparative Example 7 Filter Material of Comparative Example 3 0.25 3.3 7460 Example 6 Filter Material of Example 3 0.25 1.7 8150 Comparative Example 8 Filter Material of Comparative Example 4 0.43 2.1 4100 As is clear from Table 2, Example 4 and Comparative Examples 5, 6, and Comparing Example 5 with Comparative Example 7 and Example 6 with Comparative Example 8, the pleated cartridge filters of the respective examples using the filter medium of the present invention were slightly different from those of the respective comparative examples in terms of collection ability. Excellent, with lower flow resistance and higher flow rate , Filtration life is very long.

Examples 7 and 8, Comparative Examples 9 to 11 (Deep Type Cartridge Filters) Seven types of filter media Nos. 1 and 3 to 8 shown in Table 3 below having different basis weights of 80 g / m ^{2 having} different average pore diameters by the melt blow method. A polypropylene mettleblown nonwoven fabric was produced. Further, the filter media No. 2 includes Examples 1 and 3 and Comparative Examples 1, 2, and 4.
Was used. These filter media were sequentially wound and laminated on a porous core in the order of the filter media number to produce a depth type cartridge filter having an inner diameter of 3 cm, an outer diameter of 6.4 cm, and a length of 25 cm.

[0030]

Table 3 Filter medium number 1 2 3 4 5 6 7 8 Average pore diameter [μm] 70 1.0 to 1.2 3 5 10 17 24 31 Roll length [cm] 180 60 60 60 40 40 40 40 30

Example 9 and Comparative Example 12 (Deep type cartridge filter) Seven types of polypropylene non-woven fabric made of polypropylene having a basis weight of 80 g / m ^{2 and} different average pore sizes of filter media Nos. 1 and 3 to 8 shown in Table 4 below by a melt blow method. Was prepared. In addition, the filter media obtained in Example 2 and Comparative Example 3 were used as the filter media No. 2. These filter media were sequentially wound and laminated on a porous core in the order of the filter media number to produce a depth type cartridge filter having an inner diameter of 3 cm, an outer diameter of 6.4 cm, and a length of 25 cm.

[0032]

Table 4 Filter medium number 1 2 3 4 5 6 7 8 Average pore diameter [μm] 70 2.2 to 2.3 5 10 17 24 31 62 Roll length [cm] 180 60 60 60 40 40 40 40 30 Examples 7 to 9 and comparison The display cartridge filters of Examples 9 to 12 were mounted on the housing of the liquid filtration apparatus, and the filtration performance was examined by the following method. The results are shown in Table 5. (Water flow resistance) Pressure loss when water was flowed through the cartridge filter at a flow rate of 10 liter / min was measured and defined as water flow resistance. (Removed particle size) While uniformly stirring a test solution having a concentration of 10 ppm in which JIS type 11 dust is dispersed in water, water is passed through the cartridge filter at a flow rate of 10 liter / minute, and the filtrate one minute after the start of water flow is collected. Then, the number of particles contained in the filtrate and the test solution before filtration was measured for each particle using a particle size distribution analyzer, and the collection efficiency at each particle size was determined by the following equation. Among the particle diameters showing 100% collection efficiency,
The smallest particle size (μm) was taken as the particle size removed by the cartridge filter. Collection efficiency (%) = (AB) × 100 / A Here, A is the number of particles before filtration, and B is the number of particles after filtration. (Filtration life) Concentration of JIS 11 dust dispersed in water 1
While uniformly stirring the test solution of 0 ppm, water was passed through the cartridge filter at a flow rate of 10 liters / minute, and the pressure loss was measured sequentially for each flow rate, and the differential pressure from the initial pressure was 2 kg / cm ² . The total amount of water that had been processed until this time was determined as the filtration life.

[0033]

[Table 5] Filter media No. 2 Water flow resistance Removal particle size Filtration life Filter media used [kg / cm ² ] [μm] [liter] Example 7 Filter media of Example 1 1.06 0.51 1850 Comparative Example 9 Comparison Filter material of Example 1 1.59 0.53 1050 Comparative example 10 Filter material of Comparative example 2 1.65 0.50 965 Example 8 Filter material of Example 3 1.02 0.52 1920 Comparative example 11 Filter material 1 of Comparative example 4 .64 0.51 980 Example 9 Filter medium of Example 2 0.80 0.92 2670 Comparative Example 12 Filter medium of Comparative Example 3 1.34 0.90 1425 As is clear from Table 5, Example 7 and Comparative Example 9, 10,
Comparing Example 8 with Comparative Example 11 and Example 9 with Comparative Example 12, the depth type cartridge filter of each Example using the filter medium of the present invention is more excellent in the collecting ability than those of Comparative Examples. Equivalent, but with lower water flow resistance, higher throughput and very long filtration life.

[0034]

Since only a small pressure is applied to the nonwoven fabric A under the pressure treatment conditions of the present invention, the nonwoven fabric A is not densified so much, and the nonwoven fabric B which has been previously subjected to pressure and heat treatment is used.
And a filter medium having a structure with a difference in density is obtained. Therefore, the filter medium of the present invention has a coarse-dense structure and a low density, so that the filtration accuracy is high, the processing flow rate is large, and the filtration life is long. Also,
Since the filter medium of the present invention has a layer having high filtration accuracy and a layer coarser than that, it is difficult to be clogged,
It has a long life and excellent collection efficiency. In particular, the filter medium of the present invention is effective and useful when used as a filter medium for a pleat cartridge or a depth cartridge.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-142421 (JP, A) JP-A-4-313312 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 39/00-39/20

Claims (7)

(57) [Claims] 1. A nonwoven fabric A made of fibers having an average fiber diameter of 0.1 to 10 μm and a nonwoven fabric B obtained by heating and pressing a nonwoven fabric made of fibers having an average fiber diameter of 0.1 to 10 μm,
A non-woven fabric A and a non-woven fabric B having a dense and dense structure, wherein the non-woven fabric B and the non-woven fabric B are pressure-treated under a pressure condition smaller than that of the heating and pressure treatment of the non-woven fabric B after heating. 2. The filter medium according to claim 1, wherein the nonwoven fabric A and / or the nonwoven fabric B is a melt blown nonwoven fabric. 3. The filter medium according to claim 1, wherein the nonwoven fabric A and / or the nonwoven fabric B is a hydroentangled nonwoven fabric mainly composed of splittable fibers. 4. The non-woven fabric A or non-woven fabric B is one of a melt blown non-woven fabric and the other is a hydro-entangled non-woven fabric mainly composed of splittable fibers.
3. The filter medium according to item 1. 5. The filter medium according to claim 1, wherein the fibers constituting the nonwoven fabric A and / or the nonwoven fabric B have an average fiber diameter of 0.5 to 5 μm. 6. The nonwoven fabric A and the nonwoven fabric B have the same or substantially the same average fiber diameter.
The filter medium according to any one of the above. 7. A nonwoven fabric A composed of fibers having an average fiber diameter of 0.1 to 10 μm and a nonwoven fabric B obtained by heating and pressing a nonwoven fabric composed of fibers having an average fiber diameter of 0.1 to 10 μm,
A method for producing a filter material having a dense and dense structure in which nonwoven fabric A and nonwoven fabric B are integrated, wherein after heating, nonwoven fabric B is subjected to pressure treatment under a pressure condition smaller than the pressure condition of the heat and pressure treatment.