阅读说明：本技术 一种聚氯乙烯糊树脂及其制备方法 (Polyvinyl chloride paste resin and preparation method thereof ) 是由 张建君 刘书霞 田鹏 郭孝伟 于 2021-06-17 设计创作，主要内容包括：本发明公开了一种聚氯乙烯糊树脂及其制备方法,所述聚氯乙烯糊树脂成分如下：聚氯乙烯99.0-99.022％、十二烷基硫酸钠0.7-0.734％、焦亚硫酸钠0.093-0.0938％、水0.1-0.15％、过硫酸钾、聚氧乙烯辛烷基苯酚醚和碳酸氢钠混合物0.000002-0.107％,在反应釜中加入脱盐水、活化剂、乳化剂等,真空环境下加入定量的引发剂焦亚硫酸钠、氯乙烯单体,控制釜内温度搅拌反应一段时间制备种子乳液；其次,在聚合釜中加入脱盐水、活化剂、乳化剂等,真空环境下加入定量的引发剂焦亚硫酸钠、种子、氯乙烯单体,控制釜内温度搅拌进行聚合反应。本发明树脂产品具有聚合度高、糊粘度低、塑化快速、透明性好、脱泡性能好的特点,采用该糊树脂制得的制品透明性好,机械强度高。(The invention discloses a polyvinyl chloride paste resin and a preparation method thereof, wherein the polyvinyl chloride paste resin comprises the following components: 99.0-99.022% of polyvinyl chloride, 0.7-0.734% of sodium dodecyl sulfate, 0.093-0.0938% of sodium metabisulfite, 0.1-0.15% of water, 0.000002-0.107% of potassium persulfate, polyoxyethylene octyl phenol ether and sodium bicarbonate mixture, adding desalted water, an activating agent, an emulsifying agent and the like into a reaction kettle, adding a certain amount of initiator sodium metabisulfite and a vinyl chloride monomer under a vacuum environment, and controlling the temperature in the kettle to stir and react for a period of time to prepare seed emulsion; secondly, desalted water, an activating agent, an emulsifying agent and the like are added into a polymerization kettle, a certain amount of initiator sodium metabisulfite, seeds and vinyl chloride monomer are added under a vacuum environment, and the temperature in the kettle is controlled to stir for polymerization reaction. The resin product of the invention has the characteristics of high polymerization degree, low paste viscosity, quick plasticization, good transparency and good defoaming performance, and the product prepared by adopting the paste resin has good transparency and high mechanical strength.)

1. A polyvinyl chloride paste resin characterized by: the polyvinyl chloride paste resin comprises the following components: 99.0 to 99.022 percent of polyvinyl chloride, 0.7 to 0.734 percent of sodium dodecyl sulfate, 0.093 to 0.0938 percent of sodium metabisulfite, 0.1 to 0.15 percent of water, 0.000002 to 0.107 percent of mixture of potassium persulfate, polyoxyethylene octyl phenol ether and sodium bicarbonate.

2. A polyvinyl chloride paste resin according to claim 1, wherein: the preparation method of the polyvinyl chloride paste resin comprises the following steps:

s1: seed preparation: desalted water was added to the polymerization kettle, and based on 100 mass of desalted water: regulating the pH value of 0.0084 potassium persulfate, 0.092 sodium metabisulfite and a pH regulator NH4-NH4CO3 solution, and uniformly stirring;

adding 0.092-0.109% of initiator sodium metabisulfite solution into a polymerization kettle in a vacuum environment, controlling the stirring speed in the kettle, continuously and uniformly adding vinyl chloride monomer and emulsifier sodium dodecyl sulfate solution, reacting for a certain time at 45 ℃, stopping stirring for 1h to stop the reaction, wherein the whole reaction lasts for 7-10h, and the prepared vinyl chloride polymerized microspheres with the particle size range of 0.2-0.65 micron have the solid content of 31-34%;

s2: polymerization reaction: adding a calculated amount of desalted water into a polymerization kettle, adding a copper chloride solution, potassium persulfate, a solid trace of sodium dodecyl sulfate and a pH regulator according to the proportion of seed reaction to regulate the pH, and uniformly stirring;

adding an initiator sodium metabisulfite solution, a vinyl chloride monomer and an emulsifier solution according to the proportion of seed reaction in a vacuum environment of a polymerization kettle, continuously and uniformly adding the vinyl chloride monomer and the lauryl sodium sulfate in the reaction process, adding the initiator solution when the reaction is carried out for 1/3 times of the whole time, increasing the flow rate of the lauryl sodium sulfate solution to 1.18 times of the original flow rate, respectively stopping the vinyl chloride monomer and the emulsifier sodium dodecyl sulfate solution after the reaction is continuously carried out for 8-12h at the temperature of 55-62 ℃, continuously stirring for 1h, and adding a terminator mercaptoethanol to terminate the reaction;

s3: under the condition of constant atomization and drying, the resin is atomized and dried by a dryer, and the dried product is ground to prepare paste resin with high polymerization degree, low paste viscosity, quick plasticization and good transparency.

3. A method for preparing a polyvinyl chloride paste resin according to claim 2, characterized in that: polyvinyl chloride paste resin based preparation methods S1 and S2: the ratio of the desalted water to the chloroethylene is 1.1-1.3: 1; the mass ratio of the chloroethylene to the emulsifier is 148-150: 1.

4. A method for preparing a polyvinyl chloride paste resin according to claim 2, characterized in that: polyvinyl chloride paste resin based preparation methods S1 and S2: the pH value is adjusted to 7.8-8.4.

5. A method for preparing a polyvinyl chloride paste resin according to claim 2, characterized in that: preparation method S3 based on polyvinyl chloride paste resin: the seed particle size is in the range of 0.2-0.65 micron, and the amount of vinyl chloride monomer is 62-66 times of the solid mass of the seed.

6. A method for preparing a polyvinyl chloride paste resin according to claim 2, characterized in that: preparation method S3 based on polyvinyl chloride paste resin: at 1/3 hours during the entire time the reaction was run, 10% initiator solution was added and the flow rate of the sodium lauryl sulfate solution was adjusted to 1.18 times the original flow rate.

7. A method for preparing a polyvinyl chloride paste resin according to claim 2, characterized in that: preparation method S3 based on polyvinyl chloride paste resin: sodium dodecyl sulfate and vinyl chloride monomer, T_{Length of reaction}-2h<T_{Vinyl chloride monomer}<T_{Sodium dodecyl sulfate}<T_{Length of reaction}-1h。

8. A method for preparing a polyvinyl chloride paste resin according to claim 2, characterized in that: preparation method S3 based on polyvinyl chloride paste resin: adding vinyl chloride monomer to react for 8-12h at constant temperature to finish the reaction.

Technical Field

The invention relates to the technical field of high polymer materials, in particular to polyvinyl chloride paste resin and a preparation method thereof.

Background

Polyvinyl chloride paste resins are generally prepared by emulsion and microsuspension processes, and are one type of polyvinyl chloride resin. The product can be widely used in the processing of dipping, rotary forming, coating, foaming and the like, and is the main raw material for producing floor leather, wallpaper, disposable PVC examination gloves, tarpaulin and the like.

Paste resin with high paste viscosity can not only reduce the stability of products among batches, but also increase the addition of a plasticizer, thereby increasing the processing cost and influencing the mechanical property and transparency of products; paste resin with low paste viscosity has poor defoaming performance, and a product produced by the paste resin has more pinholes, so that the appearance and the internal quality of the product are influenced.

The paste resin particles are distributed to determine paste viscosity, the paste resin with good particle form, moderate average particle size and proper particle size distribution presents bimodal distribution with proper proportion can play a role in filling small particles among large particle pores, the dosage of the plasticizer is minimum, and good paste forming performance is embodied.

Disclosure of Invention

The invention aims to provide a polyvinyl chloride paste resin and a preparation method thereof, so as to solve the problems in the background technology.

In order to achieve the purpose, the invention provides the following technical scheme: the polyvinyl chloride paste resin comprises the following components: 99.0-99.022% of polyvinyl chloride, 0.7-0.734% of sodium dodecyl sulfate, 0.093-0.0938% of sodium metabisulfite, 0.1-0.15% of water, 0.000002-0.107% of a mixture of potassium persulfate, copper chloride, mercaptoethanol and ammonium bicarbonate.

Preferably, the preparation method of the polyvinyl chloride paste resin is as follows:

s1: seed preparation: desalted water was added to the polymerization kettle, and based on 100 mass of desalted water: potassium persulfate 0.0084, sodium metabisulfite 0.092 and pH regulator NH₃-NH₄HCO₃Adjusting the pH value of the buffer solution, and uniformly stirring;

adding 0.092-0.109% of initiator sodium metabisulfite solution into a polymerization kettle in a vacuum environment, controlling the stirring speed in the kettle, continuously and uniformly adding vinyl chloride monomer and emulsifier sodium dodecyl sulfate solution, reacting for a certain time at 45 ℃, stopping stirring for 1h to stop the reaction, wherein the whole reaction lasts for 7-10h, and the prepared vinyl chloride polymerized microspheres with the particle size range of 0.2-0.65 micron have the solid content of 31-34%;

s2: polymerization reaction: adding a calculated amount of desalted water into a polymerization kettle, adding a copper chloride solution, potassium persulfate, a solid trace of sodium dodecyl sulfate and a pH regulator according to the proportion of seed reaction to regulate the pH, and uniformly stirring;

adding an initiator sodium metabisulfite solution, a vinyl chloride monomer and an emulsifier solution according to the proportion of seed reaction in a vacuum environment of a polymerization kettle, continuously and uniformly adding the vinyl chloride monomer and the lauryl sodium sulfate in the reaction process, adding the initiator solution when the reaction is carried out for 1/3 times of the whole time, increasing the flow rate of the lauryl sodium sulfate solution to 1.18 times of the original flow rate, respectively stopping the vinyl chloride monomer and the emulsifier sodium dodecyl sulfate solution after the reaction is continuously carried out for 8-12h at the temperature of 55-62 ℃, continuously stirring for 1h, and adding a terminator mercaptoethanol to terminate the reaction;

s3: under the condition of constant atomization and drying, the resin is atomized and dried by a dryer, and the dried product is ground to prepare paste resin with high polymerization degree, low paste viscosity, quick plasticization and good transparency.

Preferably, the preparation methods S1 and S2 based on polyvinyl chloride paste resin: the ratio of the desalted water to the chloroethylene is 1.1-1.3: 1; the mass ratio of the chloroethylene to the emulsifier is 148-150: 1.

Preferably, the preparation methods S1 and S2 based on polyvinyl chloride paste resin: the pH value is adjusted to 7.8-8.4.

Preferably, in the preparation method S3 based on the polyvinyl chloride paste resin: the seed particle size is in the range of 0.2-0.65 micron, and the amount of vinyl chloride monomer is 62-66 times of the solid mass of the seed.

Preferably, in the preparation method S3 based on the polyvinyl chloride paste resin: at 1/3 hours during the entire time the reaction was run, 10% initiator solution was added and the flow rate of the sodium lauryl sulfate solution was adjusted to 1.18 times the original flow rate.

Preferably, in the preparation method S3 based on the polyvinyl chloride paste resin: sodium dodecyl sulfate and vinyl chloride monomer, T_{Length of reaction}-2h<T_{Vinyl chloride monomer}<T_{Sodium dodecyl sulfate}<T_{Length of reaction}-1h。

Preferably, in the preparation method S3 based on the polyvinyl chloride paste resin: adding vinyl chloride monomer to react for 8-12h at constant temperature to finish the reaction.

Compared with the prior art, the invention has the beneficial effects that: adopting a certain proportion of emulsifier, water-based initiator, PH value regulator and other auxiliary agents to realize the polymerization of vinyl chloride monomer in water to form polyvinyl chloride emulsion; under certain reaction conditions, the emulsion is taken as a seed, and auxiliary agents such as an emulsifier, a water-based initiator, a pH value regulator and the like are added in proportion to realize secondary polymerization of the vinyl chloride monomer on the seed; and (3) spray drying the polymerized latex to obtain the polyvinyl chloride paste resin product. The average particle size of the product is 1-1.3 μm, the average polymerization degree is 1200-1600, the paste viscosity is 2500-3500mPa.s, and the particle size distribution of the primary particles is bimodal. The paste resin product has the characteristics of high polymerization degree, low paste viscosity, quick plasticization, good transparency and good defoaming performance, and products prepared by the paste resin have good transparency and high mechanical strength.

In the second stage of polymerization reaction, a small amount of initiator solution is added after the reaction is carried out for a period of time, and the flow rate of the sodium dodecyl sulfate solution is increased. In the early stage of polymerization reaction which is carried out by taking the seeds as the center, the resin particles are gradually increased on the basis of the seeds, the effective collision on the vinyl chloride monomer in the liquid is reduced, the reaction rate is reduced, and the initiator and the emulsifier are added to initiate the continuous reaction so as to meet the requirement of the continuously increased particles on the emulsifier; meanwhile, a certain amount of initiator is added to initiate a new polymerization reaction, and a proper amount of emulsifier is added to meet the requirement of new particles and prevent emulsion breaking. The newly initiated particles are smaller, the effective collision is high, the reaction rate is high, the new particles are gradually increased, the particles with the particle sizes close to those of the new particles in the system are gradually increased, the reaction rate is also gradually reduced, the system can be built to form new balance, and finally the particle size distribution of the whole system presents double peaks.

Drawings

FIG. 1 is a graph of the basic performance parameters of the product of the present invention;

FIG. 2 is a graph showing a particle size distribution of a polymer product of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front", "rear", "both ends", "one end", "the other end", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "disposed," "connected," and the like are to be construed broadly, such as "connected," which may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

Referring to fig. 1 and 2, five embodiments of the present invention are shown:

the first embodiment is as follows:

the polyvinyl chloride paste resin comprises the following components: 99.0-99.022% of polyvinyl chloride, 0.7-0.734% of sodium dodecyl sulfate, 0.093-0.0938% of sodium metabisulfite, 0.1-0.15% of water, 0.000002-0.107% of a mixture of potassium persulfate, copper chloride, mercaptoethanol and ammonium bicarbonate.

Example two:

the preparation method of the polyvinyl chloride paste resin comprises the following steps:

s1: seed preparation: desalted water was added to the polymerization kettle, and based on 100 mass of desalted water: potassium persulfate 0.0084, sodium metabisulfite 0.092 and pH regulator NH₃-NH₄HCO₃Adjusting the pH value of the buffer solution to 7.8-8.4, and uniformly stirring;

adding 0.092-0.109 of initiator sodium metabisulfite solution into a polymerization kettle in a vacuum environment, controlling the stirring speed in the kettle, continuously and uniformly adding vinyl chloride monomer and emulsifier sodium dodecyl sulfate solution, reacting for a certain time at 45 ℃, stopping stirring for 1h to stop the reaction, wherein the whole reaction lasts for 7-10h, and the ratio of desalted water to vinyl chloride is 1.1-1.3: 1; the mass ratio of the chloroethylene to the emulsifier is 148-150:1, and the prepared chloroethylene polymerized microspheres with the product particle size range of 0.2-0.65 micron have the solid content of 31-34 percent;

s2: polymerization reaction: adding a calculated amount of desalted water into a polymerization kettle, adding a copper chloride solution, potassium persulfate, a solid trace of sodium dodecyl sulfate and a pH regulator according to the proportion of seed reaction to regulate the pH value to be 7.8-8.4, and uniformly stirring;

adding an initiator sodium metabisulfite solution, a vinyl chloride monomer and an emulsifier solution according to the proportion of seed reaction in a vacuum environment of a polymerization kettle, continuously and uniformly adding the vinyl chloride monomer and lauryl sodium sulfate in the reaction process, adding the initiator solution when the reaction is carried out for 1/3 times of the whole time, increasing the flow rate of the lauryl sodium sulfate solution to 1.18 times of the original flow rate, respectively stopping the vinyl chloride monomer and the emulsifier sodium dodecyl sulfate solution after the reaction is continuously carried out for 8-12h at 55-62 ℃, continuously stirring for 1h, adding a terminator mercaptoethanol to stop the reaction, and controlling the ratio of desalted water to vinyl chloride to be 1.1-1.3: 1; the mass ratio of the chloroethylene to the emulsifier is 148-;

s3: under the conditions of constant atomization and drying, carrying out atomization and drying on the resin by a dryer, grinding the dried product to prepare paste resin with high polymerization degree, low paste viscosity, quick plasticization and good transparency, wherein the particle size range of seeds is 0.2-0.65 micron, the amount of vinyl chloride monomer is 62-66 times of the mass of the seed solid, 10% of initiator solution is added when the reaction is carried out for 1/3 times of the whole time, and the flow rate of the sodium dodecyl sulfate solution is increased to 1.18 times of the original flow rate;

sodium dodecyl sulfate and vinyl chloride monomer, T_{Length of reaction}-2h<T_{Vinyl chloride monomer}<T_{Sodium dodecyl sulfate}<T_{Length of reaction}And (5) adding vinyl chloride monomer for reacting for 8-12h at constant temperature after-1 h.

Example three:

the first step is as follows: preparation of seeds

Adding 525kg of desalted water, copper chloride, micro-solid sodium dodecyl sulfate, 0.042kg of potassium persulfate and a pH regulator into a polymerization kettle with the volume of 1 square, regulating the pH to be 7.8, and uniformly stirring;

adding 0.46kg of initiator sodium metabisulfite solution into a polymerization kettle in a vacuum environment, controlling the stirring speed in the kettle, continuously and uniformly adding 390.5kg of vinyl chloride monomer and 24L of 2.75kg of solution containing emulsifier sodium dodecyl sulfate, reacting at 45 ℃ for 5 hours, stopping adding the sodium dodecyl sulfate solution, reacting for 1 hour, stirring for 1 hour, stopping reacting, and continuing the whole reaction for 7 hours.

The second step is that: polymerisation reaction

Adding 525kg of desalted water, a copper chloride solution, 0.046kg of potassium persulfate, a solid trace sodium dodecyl sulfate and a pH regulator into a polymerization kettle with the volume of 1 square, regulating the pH to be 7.8, and uniformly stirring;

adding 0.48kg of initiator sodium metabisulfite solution into a polymerization kettle in a vacuum environment, continuously and uniformly adding 418kg of vinyl chloride monomer and 2.69kg of solution containing sodium dodecyl sulfate in the seed reaction process, adding 0.048kg of solid initiator solution after 3 hours of reaction, adjusting the flow rate of the sodium dodecyl sulfate solution to 1.18 times of the original flow rate, stopping the sodium dodecyl sulfate solution after 7 hours of reaction at 56 ℃, stirring for 1 hour after 1 hour of reaction, stopping the reaction after 1 hour of stopping the addition of the vinyl chloride monomer, continuing the whole reaction for 9 hours, wherein the polymerization conversion rate reaches 85-90%, adding a terminator mercaptoethanol to stop the reaction, and obtaining the original particles with the particle size of the paste resin within the range of 0.1-1.8 microns;

the third step: drying

Under the condition of constant atomization and drying, the resin is atomized and dried by a dryer, and the dried product is ground to prepare the paste resin with high polymerization degree, low paste viscosity, quick plasticization, good transparency and good defoaming performance.

Example four:

the first step is as follows: preparation of seeds

Adding 525kg of desalted water, copper chloride, trace solid sodium dodecyl sulfate, 0.046 potassium persulfate and a pH regulator into a polymerization kettle with the volume of 1 square, regulating the pH to be 7.8, and uniformly stirring;

adding 0.520kg of initiator sodium metabisulfite into a polymerization kettle in a vacuum environment, controlling the stirring speed in the kettle, continuously and uniformly adding 430.2kg of vinyl chloride monomer and 2.98kg of solution containing emulsifier sodium dodecyl sulfate, reacting at 45 ℃ for 4 hours, stopping adding the sodium dodecyl sulfate solution, reacting for 1 hour, stirring for 1 hour, stopping reacting, and continuing the whole reaction for 5 hours.

The second step is that: polymerisation reaction

Adding 525kg of desalted water, 0.2% copper chloride solution, 0.0475 potassium persulfate, a solid trace of sodium dodecyl sulfate and a pH regulator into a polymerization kettle with the volume of 1 square, regulating the pH to be 7.8, and uniformly stirring;

adding 0.521kg of initiator sodium metabisulfite into a polymerization kettle in a vacuum environment, continuously and uniformly adding 438 vinyl chloride monomer and a solution containing 3.04kg of sodium dodecyl sulfate in the reaction process, adding 0.0521kg of initiator into the solution after 3 hours of reaction, increasing the flow rate of the sodium dodecyl sulfate solution to 1.18 times of the original flow rate, stopping the sodium dodecyl sulfate solution after 7.5 hours of reaction at 58 ℃, stirring the mixture for 1 hour after 0.5 hour of reaction is stopped, stopping the reaction after the vinyl chloride monomer is added, continuing the whole reaction for 9 hours, ensuring the polymerization conversion rate to be 85-90 percent, adding a terminator mercaptoethanol to stop the reaction, and obtaining the original particles with the particle size of the paste resin being in the range of 0.1-1.8 microns;

the third step: drying

Under the condition of constant atomization and drying, the resin is atomized and dried by a dryer, and the dried product is ground to prepare the paste resin with high polymerization degree, low paste viscosity, quick plasticization, good transparency and good defoaming performance.

Example five:

the first step is as follows: preparation of seeds

Adding 525kg of desalted water, 0.2% copper chloride, a trace amount of sodium dodecyl sulfate solid, 0.047kg of potassium persulfate and a pH regulator into a polymerization kettle with the volume of 1 square, regulating the pH to be 7.8, and uniformly stirring;

adding 0.535kg of initiator sodium metabisulfite into a polymerization kettle in a vacuum environment, controlling the stirring speed in the kettle, continuously and uniformly adding 398kg of vinyl chloride monomer and 2.884kg of solution containing emulsifier sodium dodecyl sulfate, reacting at 45 ℃ for 4 hours, stopping adding the sodium dodecyl sulfate solution, reacting for 1 hour, stopping adding the vinyl chloride monomer, stirring for 1 hour, stopping reacting, and continuing the whole reaction for 5 hours.

The second step is that: polymerisation reaction

Adding 525kg of desalted water, a copper chloride solution, 0.046kg of potassium persulfate, a solid trace sodium dodecyl sulfate and a pH regulator into a polymerization kettle with the volume of 1 square, regulating the pH to be 7.8, and uniformly stirring;

adding 0.508kg of initiator sodium metabisulfite solution into a polymerization kettle in a vacuum environment, continuously adding 419kg of vinyl chloride monomer and 2.915kg of sodium dodecyl sulfate-containing solution at a constant speed in the reaction process, adding 0.0508kg of initiator solution after reacting for 3.3h, adjusting the flow speed of the sodium dodecyl sulfate solution to 1.18 times of the original flow speed, stopping the sodium dodecyl sulfate solution after reacting for 8.5h at 62 ℃, stirring for 1h after stopping the addition of the vinyl chloride monomer after reacting for 0.5h, stopping the reaction, continuing the whole reaction for 10h, wherein the polymerization conversion rate reaches 85-90%, adding a terminator mercaptoethanol to stop the reaction, and obtaining the original particles with the particle size of the paste resin being within the range of 0.1-1.8 microns;

the third step: drying

Under the condition of constant atomization and drying, the resin is atomized and dried by a dryer, and the dried product is ground to prepare the paste resin with high polymerization degree, low paste viscosity, quick plasticization, good transparency and good defoaming performance.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.