JPH08112766A - Abrasive, manufacture thereof and polyurethane bonding agent for abrasive - Google Patents

Abstract

PURPOSE: To provide an abrasive maintaining excellent polishing performance for a long period by firmly securing a large amount of abrasive grains to prevent the grain from easily coming off when used, to provide a method of manufacturing this abrasive, and to provide a polyurethane bonding agent for the abrasive used in this method. CONSTITUTION: Polyetherpolyole and pure MDI are mixed so as to obtain a 208 index, and after sufficiently stirring two, hour reaction is performed at 70 deg.C, to obtain a bonding agent 4 composed of urethane denatured prepolymer. Thereafter, the bonding agent 4 of 800g per m<2> is applied by a brush to a surface of a polyurethane foam sheet, to scatter from above the bonding agent an aluminum oxide grain of 60 mesh mean grain size, and next after leaving alone for two minutes at an ordinary temperature, a surplus aluminum oxide grain is removed to obtain an abrasive 1.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an abrasive material in which abrasive particles are uniformly dispersed in a polishing layer and adhered in a large amount, and the particles are not easily shredded during use and excellent polishing performance is maintained for a long period of time. The present invention also relates to a polyurethane adhesive which is excellent in strength, flexibility and the like and is suitable for use as an abrasive. The abrasive of the present invention can be used for finishing woodworking, pre-coating or surface treatment of metal or the like before coating, stain removal and rust removal.

[0002]

2. Description of the Related Art Conventionally, in the use of abrasives as described above, in order to efficiently polish a cloth file, a sandpaper, a curved surface, etc., a flexible abrasive material having abrasive particles adhered to a polyurethane foam sheet or the like has been used. Are used. In all of these, abrasive particles are fixed to the surface of a substrate such as cloth or paper with an adhesive, but in order to adhere a hard object such as abrasive particles, it is generally preferable to use an adhesive having a high hardness. Usually, a phenol-based or epoxy-based adhesive is used. In addition, when the base material is a flexible material such as a foam sheet, an adhesive that is not only excellent in strength but also has good elongation and is appropriately flexible is used.

The above-mentioned abrasives are generally prepared by applying an adhesive to the surface of a substrate such as cloth or paper by a method such as transfer with a roller, spraying with a spray or brush coating, and then the abrasive particles on the surface of the adhesive. Is sprayed onto the surface of the base material to adhere the abrasive particles. Further, in the case where a sufficient amount of abrasive particles cannot be adhered to the surface of the base material only by the above-mentioned step, there is a product in which the same step is repeated a plurality of times to adhere more abrasive particles.

[0004]

However, a hard abrasive using an epoxy adhesive or the like has high strength but is brittle, and especially when a hard material such as metal is abraded, the abrasive particles are shed from the base material. There are many. In addition, an abrasive material using a foam sheet and a soft adhesive agent may adhere to the surface of the work material, resulting in poor workability. As described above, conventional abrasives have advantages and disadvantages, but in any case, in order to maintain excellent polishing performance for a long period of time, more abrasive particles are more firmly and uniformly adhered to the base material. There is a need to.

However, in the conventional product, the wetness of the abrasive particles scattered on the surface of the adhesive and the adhesive is not always sufficient, and even if the adhesive is applied thickly, the particles are mixed and embedded in the adhesive. It is difficult to insert, and it is difficult to fix a large amount of particles uniformly. Moreover, in the surface layer of the adhesive, wetting of the particle surface by the adhesive is insufficient, so that many abrasive particles are shed at present in a relatively short period of use. Further, as described above, there is a product in which the application of the adhesive and the spraying of the abrasive particles are repeated a plurality of times to fix more abrasive particles to the base material. Wetting does not improve, the dispersion is not uniform, and the polishing layer lacks integrity, which is not always satisfactory in the life of the polishing material.

The present invention solves the above-mentioned conventional problems, and more abrasive particles are firmly and uniformly adhered to the surface of a base material, and an excellent abrasive performance is maintained for a long period of time. And a method for manufacturing the same. In addition, it has excellent adhesive performance, is only rigid, has appropriate flexibility, suppresses shedding of abrasive particles, and has flexibility of an abrasive obtained when a urethane foam sheet or the like is used as a substrate. It is an object of the present invention to provide a urethane-based adhesive for abrasives that does not impair the properties.

[0007]

Means for Solving the Problems The present inventor has used a polyurethane foam sheet as a base material, applying various adhesives to the surface thereof, and then spraying abrasive particles to settle the abrasive particles into the adhesive, Alternatively, it was examined how much the surface of the abrasive particles was wet by the adhesive due to the penetration of the adhesive between the abrasive particles. As a result, when a polyurethane-based adhesive containing a urethane-modified prepolymer as a main component is used, wetting of abrasive particles is good, and more abrasive particles can be fixed uniformly, and an abrasive material that can withstand long-term use is obtained. They have found that they can be obtained, and have completed the present invention based on this finding.

The abrasive of the first invention is an abrasive comprising a base material and a polishing layer bonded to the surface of the base material. Abrasive particles are substantially uniformly dispersed and mixed in the polishing layer. The adhesive particles are filled between the abrasive particles and the base material and between the abrasive particles, and a part of the abrasive particles is exposed in the surface layer of the abrasive layer. The second invention is characterized in that a part of the abrasive particles is embedded in the abrasive layer.

Further, the polyurethane adhesive for abrasives of the third invention is characterized in that the urethane-modified prepolymer is a main component, and the fourth invention is that the urethane-modified prepolymer has a high molecular weight of a specific molecular weight. It is characterized in that it is composed of a component and a low molecular weight component, and the ratio of their amounts is within a specific range. The fifth to sixth inventions are characterized in that the viscosity of the adhesive is in the range of 5,000 to 15,000 centipoise at 20 ° C, and the seventh to eighth inventions are characterized in that the urethane-modified prepolymer is 100% by weight. In case,
The content of unreacted active terminal isocyanate groups is characterized by being 2 to 5% by weight.

The "base material" is not particularly limited,
In addition to conventionally used paper, cloth, etc., a synthetic resin film or a foam sheet can also be used. The synthetic resin is not particularly limited as long as it can firmly bond an adhesive such as a phenol-based adhesive or an epoxy-based adhesive. Also,
When the polyurethane adhesive for abrasives of the present invention is used, the base material is preferably made of a urethane material, and a low-foamed or unfoamed polyurethane elastomer sheet or polyurethane foam sheet can be used.

The above-mentioned "abrasive particles" are also not particularly limited, and the material, particle size, etc. are appropriately selected according to the material and shape of the work material, the surface finish of the molded product, the purpose of polishing such as rust removal, etc. Just select it. Generally, aluminum oxide, silicon carbide, zirconium oxide, etc. are often used, but other than these, artificial diamond, boron carbide, chromium oxide, iron oxide, emery, etc. can also be used.

The above "polishing layer" is formed by polishing particles and an adhesive. As such an "adhesive", an adhesive having a large adhesive strength such as a phenol-based adhesive, an epoxy-based adhesive, a urethane-based adhesive can be used, but it has excellent wettability and has appropriate flexibility. The use of adhesives based on "urethane modified prepolymer" is preferred. Especially when a polyurethane elastomer or polyurethane foam is used as the substrate, the above adhesive is suitable. This prepolymer is obtained by reacting a polyisocyanate and a polyol, and as an additive to this, a coupling agent such as a silane coupling agent, a tackifier such as phenol or rosin, an inorganic filler such as calcium carbonate or clay. It is also possible to add an agent, an antioxidant, a stabilizer such as an ultraviolet absorber, and the like to form an adhesive.

Examples of the polyisocyanate include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate and a mixture thereof (TDI), diphenylmethane-4,4'-diisocyanate (MD).
I), xylylene diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, crude TDI, crude MD
I, and isocyanate-modified products of these isocyanates, carbodiimide-modified products, and burette-modified products. Among these, MDI, crude MDI and modified products thereof are particularly preferable.

As the above-mentioned polyol, for example, water, ethylene glycol, propylene glycol, glycerin, trimethylolpropane, pentaerythritol or other polyhydric alcohol, and one or two kinds of alkylene oxide such as ethylene oxide, propylene oxide or butylene oxide. Examples include polyether polyols obtained by addition polymerization of the above, polyester polyols obtained by reacting a polycarboxylic acid and a low molecular weight polyol, polyester polyols obtained by polymerizing caprolactone, and hydroxyl group containing castor oil and the like. Higher fatty acid esters and the like can also be used. Further, a polymer polyol obtained by graft-polymerizing an ethylenically unsaturated compound such as acrylonitrile, styrene, or methylmethacrylate to the above polyol, 1,2- or 1,4-polybutadiene polyol, or a hydrogenated product thereof is also used. it can.

The "weight average molecular weight" of the "high molecular weight component" and the "low molecular weight component" constituting the urethane modified prepolymer is "4000 to 1000", respectively.
0 "and" 150 to 750 ", and the amount ratio of both components is" 85 to 95% by weight "for the high molecular weight component and" 15 to 5% by weight "for the low molecular weight component. If the molecular weight and the weight ratio are in the above ranges, the cohesive force of the adhesive after curing is sufficient, and the abrasive particles are easily mixed in the adhesive, and the adhesive easily penetrates between the abrasive particles, As in the second aspect of the invention, a part of the abrasive particles is completely embedded in the abrasive layer, and even in the surface layer, most of the surface of each particle is wet with the adhesive, which is preferable. The upper limit of the molecular weight of 10,000 in the high molecular weight component is because the polymerization itself of a high molecular weight polymer having a longer chain is difficult.

The molecular weights of the high molecular weight component and the low molecular weight component are particularly preferably in the ranges of 4750 to 7000 and 250 to 500, respectively, and the ratios of the high molecular weight component and the low molecular weight component are 88 to 92% by weight and low molecular weight component, respectively. A range of 12-8% by weight is particularly preferred. When the molecular weights and the weight ratios of the respective components are within the above ranges, the adhesive easily penetrates between the abrasive particles, the wettability is good, and the abrasive having more excellent performance can be obtained.

The "viscosity of the prepolymer at 20 ° C." is "5000 to 15000 centipoise", especially 8
If it is 000 to 12,000 centipoise, wetting of the polishing particles is improved, and a polishing layer having high strength is formed as in the above. Further, as in the seventh to eighth inventions, the "content of unreacted active terminal isocyanate group" is 1 weight of the prepolymer.
When it is set to 00% by weight, if it is in the range of "2 to 5% by weight", a moderately flexible and tenacious polishing layer is formed, and the polishing performance of the abrasive and the durability during use are improved. Is 3 to 4% by weight, when a polyurethane foam substrate is used, the hardness of the polishing layer to be formed is similar to that of the substrate, and polishing having a better performance in polishing curved surfaces and the like. The material is obtained.

In the method for manufacturing an abrasive according to the ninth to eleventh aspects of the invention, the simple steps of applying an adhesive to a base material and spraying abrasive particles are performed, and the adhesive application and the particle spraying are each performed once. It is characterized in that a polishing layer in which abrasive particles are uniformly dispersed in the adhesive can be formed only by performing the above. According to the manufacturing method of the present invention, the thickness of the polishing layer can be arbitrarily set by the coating thickness of the adhesive, and more particles can be fixed by increasing the thickness of the polishing layer. Further, it is possible to obtain a polishing layer in which the adhesive and the polishing particles are uniformly mixed regardless of the layer thickness.

[0019]

With respect to the abrasive material of the present invention and the conventional abrasive material, the difference between the situation immediately after the application of the abrasive particles to the surface of the adhesive applied to the base material and the time after a while has been explained with reference to the drawings. The action of the adhesive in the abrasive of the present invention will be clarified. 1, (a) and FIG. 2, (a) schematically show the state of the abrasive of the present invention and the conventional product immediately after the dispersion of abrasive particles, and there is almost no difference between them. However, the situation after the adhesive has hardened over time is shown in FIG.
(B) and FIG. 2, (b) [The state after removing the abrasive particles that could not contact the adhesive and were not fixed to the substrate is shown. ] Makes a big difference.

As is apparent from FIGS. 1 (b) and 1 (b), in the abrasive material of the present invention, the adhesive easily wets the abrasive particles, so the coating thickness of the adhesive is appropriately increased and an excessive amount of the abrasive particles is dispersed. By doing so, some of the particles are easily embedded in the adhesive, and in the surface layer, the adhesive easily penetrates between the particles, so many parts of each particle surface come into contact with the adhesive and bond. To be done. Due to the action of such an adhesive, more abrasive particles can be fixed uniformly by one-time application of the adhesive and dispersion of the abrasive particles, and the particles of the surface layer are less likely to be shed, resulting in excellent polishing performance for a long time. It is possible to obtain an abrasive that maintains stable.

On the other hand, according to FIG. 2 (b), the amount of abrasive particles fixed to the base material is much smaller than that of the abrasive material of the present invention, and the abrasive particles are present only on the surface layer of the adhesive. A layer made of only an adhesive is formed between the base material and the abrasive particle layer. Because of this state,
In the conventional product, the abrasive particles in the outermost layer are easily removed, and the total amount of the abrasive particles is small, so that the life of the abrasive material is shortened.

[0022]

EXAMPLES The abrasives of the present invention and the polyurethane adhesives used therefor will be described more specifically with reference to production examples. In addition, in each of the following production examples, evaluation of each characteristic was performed as follows. Weight average molecular weight and ratio of high and low molecular weight components: GP
C measuring device (manufactured by Shimadzu Corporation, model "LC-4A") Viscosity: JIS K 7117 SB type Amount ratio of unreacted active terminal isocyanate groups: JIS K
1556, Tolylene diisocyanate test method

(1) Production of Adhesive for Abrasive Material Production Example 1 Polyether polyol (manufactured by Sanyo Kasei Co., Ltd., trade name "PPG2000") and pure MDI (Nippon Polyurethane Co., Ltd., trade name "Millionate MT") Was mixed so as to have an isocyanate index of 208, sufficiently stirred, and then reacted at 70 ° C. for 2 hours to obtain an adhesive composed of a urethane-modified prepolymer. The adhesive was stored in a closed container to avoid moisture.

Production Examples 2 to 10 In Production Example 1, by changing the types of polyol and polyisocyanate, the isocyanate index and the reaction conditions, adhesives made of prepolymers having different molecular weights of the respective components and different ratios thereof were produced. Table 1 shows the weight average molecular weights of the high molecular weight component and the low molecular weight component, the ratio of the amounts, the viscosity at 20 ° C., and the weight% of the unreacted active terminal isocyanate groups of the adhesive obtained in each of the above Production Examples.

[0025]

[Table 1]

(2) Production of Abrasive Material and Evaluation of Adhering Amount of Abrasive Particles A polyurethane foam sheet having a thickness of 25 mm was used as a base material, and the adhesive prepared in Production Examples 1 to 10 was applied to the surface thereof.
800 g of brush is applied per 1 m ^{2 of the} base material, and then an excessive amount of abrasive particles (aluminum oxide, manufactured by Showa Denko KK, trade name “Morundum A-40” is applied to the surface of the applied adhesive.
# 60 ”and # 60 represent that the average particle size is 60 mesh. The same applies hereinafter. ) Was sprayed. Then
After standing at room temperature for 2 minutes, excess abrasive particles were removed to obtain an abrasive. Also, Morundum A-40 # 90 and # 1
20 was used and the abrasive was manufactured in the same manner as above.

Further, using the following two types of commercially available adhesives, the adhesive application and the particle dispersion are carried out once in the same manner as above to produce an abrasive, and the adhered amount of abrasive particles is evaluated in the same manner. did. Commercially available adhesive: urethane emulsion (manufactured by Toray Industries, Inc., anionic 1-component urethane emulsion, viscosity; 30
Commercially available adhesive: urethane emulsion (manufactured by ADEKA ARGUS CORPORATION, anionic 1-component urethane emulsion, viscosity; 32600 centipoise)

The weight of the abrasive obtained as described above is measured, and the amount of the abrasive particles fixed per unit area is measured from the difference between the total weight of the base material and the adhesive measured in advance. did. The results are shown in Table 2. The abrasives 1 to 10 are abrasives using the adhesive of Production Examples 1 to 10, and
Abrasives 11 to 12 are abrasives using commercially available adhesives and, respectively. Furthermore, for comparison, commercially available file and paper file are also shown in Table 2.
It was also described in.

[0029]

[Table 2]

According to the results shown in Table 2, in each of the abrasives of the present invention, as the average particle size of the abrasive particles becomes smaller (particularly # 6).
(Between 0 and # 90), the amount of adhered particles tends to decrease, but the same tendency also applies to commercially available adhesives. It can be seen that the adhesive for abrasives easily wets the abrasive particles, and thus can fix more abrasive particles than the commercially available adhesive. Further, the commercially available file and paper file tend to have a smaller amount of sticking as compared with the commercially available adhesive, which shows that the adhesive for abrasives of the present invention has excellent performance.

As described above, all of the adhesives of Production Examples 1 to 10 have excellent performance as compared with the commercially available products, but Production Example 4 in which the high molecular weight component has a large molecular weight of 9000.
In the case of using the adhesive of No. 10, the adhered amount was slightly reduced in each particle size of the abrasive particles, and the amount ratio was as high as 97% even though the molecular weight of the high molecular weight component was not so high. When the above adhesive is used, the amount of sticking is further reduced, and in the abrasive of the present invention, the amount of sticking is relatively small. However, as compared with the case where a commercially available adhesive is used, many abrasive particles are still fixed.

(3) Evaluation of Grinding Amount and Particle Loss Abrading material 1 on the horizontal carriage 7 of the polishing tester 6 shown in FIG.
Is fixed to the lower surface of the attachment jig 8 fixed by the jig fixing arm 9 and is parallel to the abrasive material 1 and is a work material 11 (a cypress or aluminum plate-like body, and has a shape of It is a rectangle of 30 × 20 mm, and the thickness is 5 mm in the case of cypress and 1 mm in the case of aluminum.
A load 10 of 00 g is placed, the horizontal carriage 7 is moved at a speed of 12
The amount of grain removal of the abrasive 1 and the amount of grinding of the work material 11 were obtained by reciprocating 1000 times at m / min and a stroke of 100 mm. The amount of grain removal and the amount of grinding were determined by reducing the weight of the abrasive and the work material before and after polishing. The results are shown in Table 3.

[0033]

[Table 3]

From the results shown in Table 3, it can be seen that in each of the abrasives of the present invention, the amount of shedding is small regardless of whether the work material is cypress or aluminum. Further, the adhesive used for each abrasive in Table 3 is a flexible adhesive, except that the commercially available adhesive used for the abrasive 12 has high rigidity. The abrasive 12 has a large amount of grinding, and particularly when the work material is aluminum, the grinding performance is very excellent as compared with other abrasives. However, the amount of the particles removed is a value more than twice that of the abrasive 1 and the abrasive 5, and it can be seen that the initial performance is excellent, but the performance cannot be maintained for a long time. Further, the abrasive 11 using the commercially available adhesive has the same grinding performance as each of the abrasives of the present invention, but the amount of shed particles is very large, and like the abrasive 12, the performance cannot be maintained. .

As described above, all of the abrasives 1 to 10 have excellent performance, but especially, the high molecular weight component has a molecular weight of 7,000, and its ratio is 93% in Production Examples 1, 5, and 6.
It can be seen that the abrasives 1, 5 and 6 using the adhesive of No. 1 have a large amount of grinding and a small amount of grain removal, and are abrasives having a well-balanced and excellent performance. In addition, as described above, in the abrasives 4 and 10 using the adhesives of Production Examples 4 and 10 in which the adhered amount of the abrasive particles is slightly small, the amount of shedding is comparatively large for the grinding performance as compared with the other abrasives of the present invention. However, it is a polishing material having superior performance as a whole and having no defects as compared with a polishing material using a commercially available adhesive.

[0036]

According to the abrasive of the first invention, the abrasive particles are uniformly dispersed in the abrasive layer, and the individual abrasive particles are firmly fixed by the adhesive on the surface layer of the abrasive layer, that is, the abrading surface. Therefore, the amount of shedding during use is very small,
Excellent cutting performance is maintained for a long time. A second aspect of the invention is the abrasive of the first aspect, in which some of the abrasive particles are embedded in the polishing layer, and excellent performance is maintained for a longer period of time.

The adhesive for abrasives according to the third aspect of the present invention contains a urethane-modified prepolymer as a main component and has excellent adhesiveness and flexibility, and can be used as a flexible base material such as a polyurethane foam sheet. Can also be used, in addition, the fourth
In the adhesives of the inventions 8 to 8, more excellent adhesive performance is exhibited by specifying the molecular weight, the viscosity and the amount of the unreacted active terminal isocyanate group of the adhesive of the third invention.

According to the method for producing an abrasive of the ninth invention, the simple method of applying the adhesive to the base material and spraying the abrasive particles, and only applying the adhesive and spraying the abrasive particles only once, respectively. Thus, it is possible to manufacture an abrasive having a polishing layer in which a plurality of layers of a large amount of abrasive particles are uniformly dispersed and contained. Further, according to the method for manufacturing an abrasive using the specific adhesive of the tenth to eleventh inventions, a more uniform polishing layer can be easily formed.

[Brief description of drawings]

FIG. 1 shows the abrasive material of the present invention immediately after spraying abrasive particles on the surface of the adhesive (a) and after the adhesive is cured (b).
It is a schematic diagram showing the state of the polishing layer.

FIG. 2 is a schematic diagram showing a state of a polishing layer in a conventional abrasive immediately after spraying abrasive particles on an adhesive surface (a) and after the adhesive is hardened (b).

FIG. 3 is a schematic view of a polishing tester.

[Explanation of symbols]

1; abrasive, 2; substrate, 3; polishing layer, 4; adhesive, 5;
Abrasive particles, 6; polishing tester, 7; horizontal carriage, 8; mounting jig, 9; jig fixing arm, 10; load, 11;
Work material.

Claims (11)

[Claims] 1. A polishing material comprising a base material and a polishing layer bonded to the surface of the base material, wherein polishing particles are substantially uniformly dispersed and mixed in the polishing layer, and the polishing particles and the base material are mixed with each other. An abrasive material, characterized in that the space between the material and the abrasive particles is filled with an adhesive, and a part of the abrasive particles is exposed in the surface layer of the abrasive layer. 2. A part of the abrasive particles is embedded in the abrasive layer to form a plurality of abrasive particle layers.
Abrasive described. 3. A polyurethane-based adhesive for abrasives, which comprises a urethane-modified prepolymer as a main component. 4. The urethane-modified prepolymer comprises a high molecular weight component having a weight average molecular weight of 4,000 to 10,000,
It is composed of a low molecular weight component having a weight average molecular weight of 150 to 750, and when the total amount of the high molecular weight component and the low molecular weight component is 100% by weight, the high molecular weight component is 85%.
The polyurethane adhesive for abrasives according to claim 3, wherein the content of the low molecular weight component is 15 to 5% by weight. 5. The viscosity at 20 ° C. is 5000 to 150.
The polyurethane-based adhesive for abrasives according to claim 3, which has a pressure of 00 centipoise. 6. The viscosity at 20 ° C. is 5000 to 150.
The polyurethane-based adhesive for abrasives according to claim 4, which is 00 centipoise. 7. The urethane-modified prepolymer as 100
The polyurethane-based adhesive for abrasives according to claim 3, wherein the content of the unreacted active terminal isocyanate group is 2 to 5% by weight when the weight% is adopted. 8. The urethane-modified prepolymer as 100
The polyurethane-based adhesive for abrasives according to claim 4, wherein the content of the unreacted active terminal isocyanate group is 2 to 5% by weight when the weight% is adopted. 9. An adhesive is applied to the surface of a base material, and thereafter, an excessive amount of abrasive particles is sprinkled on the surface of the adhesive, and then the adhesive is cured so that excess surplus not fixed by the adhesive is applied. By removing the polishing particles, the polishing particles are substantially uniformly dispersed and mixed in the adhesive to form a polishing layer, the base material and the polishing layer are bonded, and the surface layer of the polishing layer is formed. 2. A method of manufacturing an abrasive, comprising obtaining an abrasive in which a part of the abrasive particles is exposed. 10. The method for producing an abrasive according to claim 9, wherein the adhesive is an adhesive containing a urethane-modified prepolymer as a main component. 11. The urethane-modified prepolymer comprises a high molecular weight component having a weight average molecular weight of 4,000 to 10,000,
It is composed of a low molecular weight component having a weight average molecular weight of 150 to 750, and when the total amount of the high molecular weight component and the low molecular weight component is 100% by weight, the high molecular weight component is 85%.
The method for producing an abrasive according to claim 10, wherein the content of the low molecular weight component is 15 to 5% by weight, and the low molecular weight component is 15 to 5% by weight.